function checkForm() {
  var cfrm = document.form1;
  var csum = cfrm.txSum.value;
  var cq1 = cfrm.s1.value;
  var cq2 = cfrm.s2.value;
  if(csum=='') {
    alert('You must fill in all the required fields before sending your request. ');
    return false;
  }
  if(csum!=eval(cq1)+eval(cq2)) {
    alert('You havent entered the correct answer to the sum! Please try again... ');
    return false;
  }
}