Hi everyone... i'm new to JavaScript. i'm stuck with my coding please any help will appreciate.
My problem with the coding is, when user enter the amount inside quantity box, the total amount will x the quantity(example , quantity 2 x MYR72 = MYR144) but the amount wont show up at sub-total. Other calculation like shipping cost & total (shipping cost + sub-total) all working fine. sorry for bad English & thank you in advanced.

PHP Code:
<?php
require_once 'library/config.php';
require_once 
'library/cart-functions.php';

$action = (isset($_GET['action']) && $_GET['action'] != '') ? $_GET['action'] : 'view';

switch (
$action) {
   case 
'add' :
      
addToCart();
      break;
   case 
'update' :
      
updateCart();
      break;   
   case 
'delete' :
      
deleteFromCart();
      break;
   case 
'view' :
}

$cartContent getCartContent();
$numItem count($cartContent);

$pageTitle 'Shopping Cart';
require_once 
'include/header.php';

// show the error message ( if we have any )
displayError();

if (
$numItem ) {
?>
<head>




<script type="text/javascript">

<!-- Begin
function  doMath() {
var one = eval(document.getElementById('txtQty[]').value) //one = quantity 
var price = 0;
var state = document.frmCart.state.value;

//alert(one);

if(state == "east"){
   if (one == 1){
      price = 6;
   }
   else if (one == 2){
      price = 8;
   }
   else if (one == 3){
      price = 10;
   }
   else if (one == 4){
      price = 12;
   }
   else if (one == 5){
      price = 12.50;
   }
   else if (one == 6){
      price = 13;
   }
   else if (one == 7){
      price = 14;
   }
   else if (one == 8){
      price = 0;
   }
   
}

else if(state == "west"){
   if (one == 1){
      price = 9.30;
   }
   if (one == 2){
      price = 12;
   }
   if (one == 3){
      price = 17.25;
   }
   if (one == 4){
      price = 20;
   }
   if (one == 5){
      price = 21;
   }
   if (one == 6){
      price = 22;
   }
   if (one == 7){
      price = 23.45;
   }
   if (one == 8){
      price = 0;
   }
}


document.getElementById('ct_qty').innerText; // pd_price * ct_qty



//document.frmCart.amount.innerText=price;
document.getElementById('amount').innerText =  price;
//alert("asdf");
var test = document.getElementById('subtotal').innerText;
//alert(test);
test = test.substring(3);
//alert(test);
document.getElementById('total').innerText =   price + parseInt(test);
}
//function custRound(x,places) {
//return (Math.round(x*Math.pow(10,places)))/Math.pow(10,places)
//}
//  End -->s
   
   
</script>
</head>


<body onLoad="MM_preloadImages('../images/btn_home_roll.gif','../images/btn_about_roll.gif','../images/btn_bloomingcare_roll.gif','../images/btn_promotion_roll.gif','../images/btn_contactus_roll.gif'), doMath()" >



<table width="900" border="0" align="center" cellpadding="0" cellspacing="0"><tr><td align="center"><table width="900" border="0" align="center" cellpadding="0" cellspacing="0"><tr><td align="center" bgcolor="#b6df51"><table width="800" border="0" cellspacing="0" cellpadding="0"><tr><td align="center"><table width="900" border="0" align="center" cellpadding="0" cellspacing="0">

  <tr>
    <td align="center"><table width="900" border="0" align="center" cellpadding="0" cellspacing="0">
      <tr><form action="<?php echo $_SERVER['PHP_SELF'] . "?action=update"?>" method="post" name="frmCart" id="frmCart">
        <td align="center" bgcolor="#b6df51"><table width="800" border="0" cellspacing="0" cellpadding="0" >
          <tr>
            <td align="left"><img src="images/title_purchase_online.gif" width="280" height="25" /></td>
          </tr>
          <tr>
            <td>&nbsp;</td>
          </tr>
          <tr>
            <td align="center"><table width="800" border="0" cellspacing="0" cellpadding="0">
              <tr>
                <td><table width="800" border="0" cellpadding="0" cellspacing="0" bgcolor="#3b7b37">
                  <tr>
                    <td width="15"><img src="images/title_box_left.gif" width="15" height="30" /></td>
                    <td width="770"><table width="770" border="0" cellspacing="0" cellpadding="0">
                      <tr>
                        <td width="170" align="center" class="yellow_txt"><strong>Item</strong></td>
                        <td width="213" align="center">&nbsp;</td>
                        <td width="141" align="center"><strong class="yellow_txt">Unit Price</strong></td>
                        <td width="106" align="center"><strong class="yellow_txt">Quantity</strong></td>
                        <td width="110" align="center"><strong class="yellow_txt">Total</strong></td>
                        <td width="30" align="center">&nbsp;</td>
                        </tr>
                    </table></td>
                    <td width="15"><img src="images/title_box_right.gif" width="15" height="30" /></td>
                  </tr>
                </table></td>
              </tr>
              
<?php
$subTotal 
0;
for (
$i 0$i $numItem$i++) {
   
extract($cartContent[$i]);
   
$productUrl "other_products.php?c=$cat_id&p=$pd_id";
   
$subTotal += $pd_price $ct_qty;
?>
              
              <tr>
                <td>&nbsp;</td>
              </tr>
              <tr>
                <td align="center"><table width="770" border="0" cellspacing="0" cellpadding="0">
                  <tr>
                    <td width="170" align="center" class="yellow_txt"><table width="150" border="0" cellpadding="0" cellspacing="0" bgcolor="#FFFFFF">
                      <tr>
                        
        
                      </tr>
                      <tr>
                        
                        <td width="116" align="center" valign="top" bgcolor="#b6df51"><a href="<?php echo $productUrl?>"><img src="<?php echo $pd_thumbnail?>" width="116" height="116" border="0" /></a><a href="<?php echo $productUrl?>"></a></td>
                        
                      </tr>
                      <tr>
                       
       
                      </tr>
                    </table></td>
                    <td width="220" align="left" class="green_txt"><strong><a href="<?php echo $productUrl?>" style="text-decoration: none"><font color="000000"><?php echo  $pd_name?></font></a></strong></td>
                    <td width="128" align="center"><strong class="black_txt"><?php echo displayAmount($pd_price); ?></strong></td>
                    <td width="112" align="center"><input name="txtQty[]"  type="text" id="txtQty[]" size="5" value="<?php echo $ct_qty?>" class="box" onKeyUp="checkNumber(this);">
  <input name="hidCartId[]" type="hidden" value="<?php echo $ct_id?>">
  <input name="hidProductId[]" type="hidden" value="<?php echo $pd_id?>"></td>
                    <td width="110" align="center"><strong class="black_txt" id="ct_qty"><?php echo displayAmount($pd_price $ct_qty); ?></strong></td>
                   <td width="30" align="center" valign="middle"><a href="#"> <img src="images/btn_delete.png" width="16" height="16" border="0" onClick="window.location.href='<?php echo $_SERVER['PHP_SELF'] . "?action=delete&cid=$ct_id"?>';" /></a>                  </tr>
                </table></td>
              </tr>
              
<?php
}
?>

              <tr>
                <td>&nbsp;</td>
              </tr>
              <tr>
                <td><table width="800" border="0" cellspacing="0" cellpadding="0">
                  <tr>
                    <td width="13" height="13"><img src="images/text_box_big_left1.gif" width="13" height="13" /></td>
                    <td width="774" height="13" bgcolor="#ffde00"><span class="style10"><img src="images/spacer.gif" width="13" height="13" /></span></td>
                    <td width="13" height="13"><img src="images/text_box_big_right1.gif" width="13" height="13" /></td>
                  </tr>
                  <tr>
                    <td bgcolor="#ffde00">&nbsp;</td>
                    <td height="50" align="center" bgcolor="#ffde00"><table width="770" border="0" cellspacing="0" cellpadding="0">
                      <tr>
                        <td width="132" align="center" class="yellow_txt">&nbsp;</td>
                        <td width="147" align="left" class="green_txt">&nbsp;</td>
                        <td width="113" align="center">&nbsp;</td>
                        <td width="102" align="center" class="black_txt"><strong>Sub-total</strong></td>
                        <td colspan="2" align="center"><strong class="black_txt" id="subtotal"><?php echo displayAmount($subTotal); ?></strong></td>
                        <td width="19" align="center" valign="middle">&nbsp;</td>
                      </tr>
                      <tr>
                        <td colspan="7" align="center" class="yellow_txt"><img src="images/spacer.gif" width="10" height="10" /></td>
                        </tr>
                      
   
                        
<!-------------------------------------------- shipping cost--------------------------------------------------->


                      <tr>
                        <td align="center" >&nbsp;</td>
                        <td align="left" class="green_txt">&nbsp;</td>
                        <td> </td>
                        <td align="center" class="black_txt"><strong>State</strong></td>
                        <td colspan="2" align="center">   <select name="state">
                    <option value="east" selected>East Malaysia</option>
                    <option value="west">Peninsular Malaysia</option>
                     </select>   </td>
                        <td align="center" valign="middle">&nbsp;</td>
                      </tr>
    
    
    <tr>
                        <td colspan="7" align="center" class="yellow_txt"><img src="images/spacer.gif" width="10" height="10" /></td>
                        </tr>
                         <tr>
                        <td align="center" class="yellow_txt">&nbsp;</td>
                        <td align="left" class="green_txt">&nbsp;</td>
                        <td align="center">&nbsp;</td>
                        <td align="center" class="black_txt"><strong>Shipping</strong></td>
                        
                        <td width="132" align="right"> <strong class="black_txt">
                          MYR</strong><!--<input type="text" name="amount" disabled="disabled" size="17" style="background-color:transparent;" border="none" >--></td>
                        
                        
                        <td width="121" align="left"><strong class="black_txt">
                          <div name="amount" id="amount"> 0</div></strong></td>
                        <td align="center" valign="middle">&nbsp;</td>
                      </tr>
                   <tr>
                        <td align="center" class="yellow_txt">&nbsp;</td>
                        <td align="left" class="green_txt">&nbsp;</td>
                        <td align="center">&nbsp;</td>
                        <td align="center" class="black_txt33">                        </td>
                        <td colspan="2" align="center" class="black_txt33">
                        <font color="#FF0000">*Purchases of 8 boxes onwards free delivery charges.</font>                        </td>
                        <td align="center" valign="middle">&nbsp;</td>
                      </tr>


<!------------------------------------------------------------------------------------------------------>    
                      
                      
                      <tr>
                        <td colspan="7" align="center" class="yellow_txt"><img src="images/spacer.gif" width="10" height="10" /></td>
                        </tr>
                      <tr>
                        <td align="center" class="yellow_txt">&nbsp;</td>
                        <td align="left" class="green_txt">&nbsp;</td>
                        <td align="center">&nbsp;</td>
                        <td align="center" class="black_txt"><strong>Total</strong></td>
                        <td width="132" align="right"> <strong class="black_txt">
                          MYR</strong><!--<input type="text" name="amount" disabled="disabled" size="17" style="background-color:transparent;" border="none" >--></td>
                        
                        
                        <td colspan="2" align="left"><strong class="black_txt" id="total"><?php echo displayAmount($subTotal);// + $shopConfig['shippingCost']); ?></strong>                        </td>
                        
                        <td width="4" align="center" valign="middle">&nbsp;</td>
                      </tr>
                      <tr>
                        <td colspan="7" align="center" class="yellow_txt"><img src="images/spacer.gif" width="10" height="10" /></td>
                        </tr>
                      <tr>
                        <td align="center" class="yellow_txt">&nbsp;</td>
                        <td align="left" class="green_txt">&nbsp;</td>
                        <td align="center">&nbsp;</td>
                        <td align="center">&nbsp;</td>
                        <td colspan="2" align="center"><input type="button" class="update_btn" src="images/btn_update_cart.gif" width="102" height="22" border="0"  name="btnUpdate" id="btnUpdate" onClick="doMath()"><!--value="submit"--></td>
                        <td align="center" valign="middle">&nbsp;</td>
                      </tr>
                    </table></td>
                    <td bgcolor="#ffde00">&nbsp;</td>
                  </tr>
                  <tr>
                    <td width="13" height="13"><img src="images/text_box_big_left2.gif" width="13" height="13" /></td>
                    <td bgcolor="#ffde00"><span class="style10"><img src="images/spacer.gif" width="13" height="13" /></span></td>
                    <td width="13" height="13"><img src="images/text_box_big_right2.gif" width="13" height="13" /></td>
                  </tr>
                  <tr>
<td>&nbsp;</td>
</tr>
                </table></td>
              </tr>
              <tr>


<?php

$shoppingReturnUrl 
= isset($_SESSION['shop_return_url']) ? $_SESSION['shop_return_url'] : 'other_products.php';
?>
              <tr>
             
                <td align="center"><table width="340" border="0" cellspacing="0" cellpadding="0">
                  <tr>
                  <td>&nbsp;</td>
                    <td><a href="#"> <img src="images/btn_continue_shopping.gif" width="162" height="22" border="0" onClick="window.location.href='<?php echo $shoppingReturnUrl?>';" /></a></td>
                    
                
<?php 
if ($numItem 0) {
?> 

                    <td width="20">&nbsp;</td>
                    <td><a href="#"> <img src="images/btn_continue_checkout.gif" width="162" height="22" border="0" onClick="window.location.href='checkout.php?step=1';"/></a></td>
                    
                  
                   
<?php
}
?> 
                  </tr>
                </table></td>
              </tr>
            </table></td>
          </tr>
          <tr>
            <td align="center">&nbsp;</td>
          </tr>
        </table></td></form>
      </tr>
      
                 

      
    </table></td>
  </tr>
</table>  
          </tr>
</table></td>
      </tr>
</table></td>
  </tr>


</body>
</html>