// JavaScript Document
function calculate(){
	var sf1 = document.calculator.sf1.value;;
	var sf2 = document.calculator.sf2.value;
	var stalls = document.calculator.stalls.value;
	var tsf = eval(sf1)*eval(sf2);
	var tblocks = (eval(tsf)*eval(stalls))/3;
	document.calculator.tblocks.value=tblocks;
	document.calculator.quantity.value=tblocks;
}