How to do summation of product of two input values

I am unable to do summation of the subtotal from the clone table input values.
Here is working fiddle: http://jsfiddle.net/rKjbg/

var $to_clone = $('.tr_clone').first().clone();

$("table").on('click', 'input.tr_clone_add', function () {
    var $tr    = $(this).closest('.tr_clone');
    var $clone = $to_clone.clone();
    $clone.find(':text').val('');
    $tr.after($clone);
});

$("table").on('click', 'input.tr_clone_remove', function () {
    var $tr    = $(this).closest('.tr_clone');
    $tr.remove();
});

$(document).on("keyup", ".quantity, .price", function(){
    var prtCont = $(this).parent().parent();
    var prce = parseInt(prtCont.find('.price').val()) - 0;
    var qnty = parseInt(prtCont.find('.quantity').val()) - 0;
    if(!isNaN(prce) && !isNaN(qnty)){
        prtCont.find('.subtotal').val(prce * (qnty));
    }else{
        prtCont.find('.subtotal').val("");
    }
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<table width="100%" border="0"  >
<tr>
    <td>Item</td>
    <td>Quantity</td>
    <td>U$ Price</td>
<td>Subtotal</td>
    <td>Add</td>
    <td>Remove</td>
</tr>
<tr class="tr_clone">
    <td>
        <select style="width:200px" name="itens[]">
        <option value="0"></option>
        <option value="1">Item A</option>
        <option value="2">Item B</option>
        <option value="3">Item C</option>
    </td>                                            
    <td><input type="text" size="5" maxlength="5" name="qtd" class="quantity text ui-widget-content ui-corner-all"></td>
    <td><input type="text" size="10" maxlength="10" name="price" class="price text ui-widget-content ui-corner-all"></td>
    <td><input type="text" size="10" maxlength="10" name="subtotal" class="subtotal text ui-widget-content ui-corner-all"></td>
    <td><input type="button" name="add" value="Add" class="tr_clone_add"></td>
    <td><input type="button" name="remove" value="Remove" class="tr_clone_remove"></td>
</tr>
</table>

I have created a function updateTotalOfSubTotal() which should be called on every trigger that happens. In your case, its keyup. You can call updateTotalOfSubTotal at other triggers too.

Here is the updated code that would give you total of subtotal:

var $to_clone = $('.tr_clone').first().clone();

$("table").on('click', 'input.tr_clone_add', function() {
  var $tr = $(this).closest('.tr_clone');
  var $clone = $to_clone.clone();
  $clone.find(':text').val('');
  $tr.after($clone);
});

$("table").on('click', 'input.tr_clone_remove', function() {
  var $tr = $(this).closest('.tr_clone');
  $tr.remove();
  updateTotalOfSubTotal();
});

$(document).on("keyup", ".quantity, .price", function() {
  var prtCont = $(this).parent().parent();
  var prce = parseInt(prtCont.find('.price').val()) - 0;
  var qnty = parseInt(prtCont.find('.quantity').val()) - 0;
  if (!isNaN(prce) && !isNaN(qnty)) {
    prtCont.find('.subtotal').val(prce * (qnty));
  } else {
    prtCont.find('.subtotal').val("");
  }
  updateTotalOfSubTotal();
});

function updateTotalOfSubTotal() {
  var totalPoints = 0;
  $(".subtotal").each(function() {
    if (parseInt($(this).val()))
      totalPoints += parseInt($(this).val());
  });
  $(".totalOfSubTotal").text(totalPoints);
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<table width="100%" border="0">
  <tr>
    <td>Item</td>
    <td>Quantity</td>
    <td>U$ Price</td>
    <td>Subtotal</td>
    <td>Add</td>
    <td>Remove</td>
  </tr>
  <tr class="tr_clone">
    <td>
      <select style="width:200px" name="itens[]">
        <option value="0"></option>
        <option value="1">Item A</option>
        <option value="2">Item B</option>
        <option value="3">Item C</option>
    </td>                                            
    <td><input type="text" size="5" maxlength="5" name="qtd" class="quantity text ui-widget-content ui-corner-all"></td>
    <td><input type="text" size="10" maxlength="10" name="price" class="price text ui-widget-content ui-corner-all"></td>
    <td><input type="text" size="10" maxlength="10" name="subtotal" class="subtotal text ui-widget-content ui-corner-all"></td>
    <td><input type="button" name="add" value="Add" class="tr_clone_add"></td>
    <td><input type="button" name="remove" value="Remove" class="tr_clone_remove"></td>
</tr>
</table>
<div class="totalOfSubTotal"></div>