This is the page I made up and it appears to work. I added some validation in because without it, if one of the variables is empty it errors out.
Code:
<HEAD>
<TITLE>Fence post calculator</TITLE>
</HEAD>
<BODY>
<p>
<FORM action="" Method="Post">
Spacing between posts:<INPUT type="text" name="fPostSp"><BR>
Ammount of paces:<INPUT type="text" name="fPaceAm"><BR>
Size of paces:<INPUT type="text" name="fPaceSz"><BR><BR>
<INPUT type="Submit" value="Calculate">
</FORM>
</p>
<%
dim PostNo 'The variable for the number of posts
dim PostSp 'The variable for spacing between posts
dim PaceAm 'The variable for the amount of paces
dim PaceSz 'The variable for the size of the paces
PostSp = Request.Form("fPostSp")
PaceAm = Request.Form("fPaceAm")
PaceSz = Request.Form("fPaceSz")
If PostSP > 0 And PaceAm > 0 And PaceSz > 0 Then
PostNo = PaceAm*PaceSz
PostNo=PostNo/PostSp
%>
<p><%=PostNo%> required posts.</p>
<%End If%>
</BODY>