help adding 3 text box values and show in a 4th

help adding 3 text box values and show in a 4th

Good Afternoon every one

    I'm very new to jquery and javascript I have 3 text boxes that I need to add up there values and display the result in a 4th textbox I have a functiion that I got from a friend but it's not calculating the 2nd textbox value which is populated form a total of a table column

I've tried every thing and cannot get this to work here is the code

  1. <script type="text/javascript">
    $(function () {
          var textBox1 = $('input:text[id$=tij]').keyup(foo);
          var textBox2 = $('input:text[id$=ptotal]').keyup(foo);
          var textBox3 = $('input:text[id$=labor]').keyup(foo); //this amount comes from a tabal column total
      function foo() {
         var value1 = textBox1.val();
         var value2 = textBox2.val();
         var value3 = textBox3.val();
         var sum = add(value1, value2, value3);
         
            $('input:text[id$=jbtotal]').val("$" +sum+".00"); }
     function add() {
         var sum = 0;
           for (var i = 0,
            j = arguments.length; i < j; i++) {
            if (IsNumeric(arguments[i])) {
            sum += parseFloat(arguments[i]); }
            } return sum; }
            function IsNumeric(input) {
            return (input - 0) == input && input && input.length > 0; } });
     
     </script>