function addqty(tbox) {
  el = document.getElementById(tbox);
  c = eval(el.value);
  c=c+1;
  el.value= c;
}
function redqty(tbox) {
  el = document.getElementById(tbox); 
  c = eval(el.value)
  if (el.value > 0) c=c-1;
  el.value= c; 
}