<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head>
<script>
function raschet_metall()
{
var a1= Number(document.form1.visota.value);
var a2= Number(document.form1.shirina.value);
var a3= Number(document.form1.dlina.value);
var b4= Number(document.form1.tol_metalla.value);
var s1=a1*a2*2;
var s2=a2*a3*2;
var s3=a1*a3*2;
var s=s1+s2+s3;
var v=s*b4*0.00000785;
document.form1.res_metall.value=v;
return s;
}
</script>
</head>
<body>
<form name="form1">
<input type="text" name="visota" /><br/>
<input type="text" name="shirina" /><br/>
<input type="text" name="dlina" /><br/>
<input type="text" name="tol_metalla" /><br/>
<input type="button" onclick="this.value = raschet_metall()" /><br/>
<input type="text" name="res_metall" />
</form>
</body>
</html>
А в чём собственно проблема?