Hello

I have attempted to make a Simple Interest Calculator using html forms and javascript and got stuck some where.Here the main problem is alert box does not pop up when i click the calculate interest button

Code:<html> <head>Calculator Simple Interest <script> var p=document.getElementById("pa"); var n=document.getElementById("ny"); var r=document.getElementById("ri"); function si() { var s; s=(p*n*r)/100; alert("Total Amount is"+s); } function ta() { var t; t=p+s; alert("Total Amount is"+t); } </script> </head> <title>Simple Interest Calculator</title> <body> <form> <b>Principal Amount</b><input type="number" id="pa"> <b>No. of years</b><input type="number" id="ny"> <b>Rate of interest</b><input type="number" id="ri"> <input type="button" onclick="si()" value="Calculate Interest"> <input type="button" onclick="ta()" value="Final Amount"> </form> </body> </html>