table calculate

HTML

<table>
    <tr>
    <td class="buyformcells buyformunitprice">$170</td>
        <td class="buyformcells buyformquantity"><input type="text" name="quantity" /></td>
    <td class="buyformcells buyformunitpricetotal"></td>
    </tr>
        <tr>
    <td class="buyformcells buyformunitprice">$170</td>
        <td class="buyformcells buyformquantity"><input type="text" name="quantity" /></td>
    <td class="buyformcells buyformunitpricetotal"></td>
    </tr>
</table>

JavaScript

$('input[name=quantity]').change(function(){
    if ($(this).attr('value').length > 0) {
         var price = parseInt($('.buyformunitprice').text().replace('$', ''));
        var quantity = parseInt($(this).attr('value'));
        var total = price * quantity;
        $('.buyformunitpricetotal').html(total);
    }
});