Jquery calculate form php

JavaScript
1

how get id=“cb<?= $i?>” ?

<script class=“jsbin” src=“http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js”></script>

<script type=“text/javascript”>

$(document).ready(
  function() {
    $('#[B]cb[/B]').change(
      function() {
        var amount = $('#principal_amount').val()*$('#principal_installment').val();
        $('#amount').val(amount);
      }
    );
  }
  );

</script>
<tr>
<td><input type=“checkbox” name=“id” value=“<?= $row2[“id_principal_payment”]?>” id=“cb<?= $i?>” onclick=“isChecked(this.checked);” />
</td>

Thx,

2

Do you want a particular one that starts with “cb” or do you want all the ones that start with “cb”