Select İnput İlişki Sorun

<select name="renk[]" multiple="renk[]"  class="btn-default btn-sm">
            <option selected value="">Seçiniz..</option>
                    <?php  include "ayar.php";  
                    $sql = mysql_query ("SELECT yil_secimi,borc_miktari FROM muhasebe_aidat_girisi2 
                    ORDER BY yil_secimi DESC"); 
                    while ($liste = mysql_fetch_array($sql)) {  ?>                
                    <option value="<?php echo $liste["borc_miktari"];?>"><?php echo $liste["yil_secimi"];?></option>    
                    <?php } ?>    
          </select>
     <input name="usertotal" />

<script type="text/javascript" src="http://cdnjs.cloudflare.com/ajax/libs/jquery/2.0.3/jquery.min.js"></script>
      <script type="text/javascript">
      var $total = $('#usertotal');
$('input,select').change(function () {
    var tot = 0;
    $('input:checkbox:checked, select > option:selected').each(function () {
        var per_op = $(this).attr('value');
        if (per_op) {
            tot += Number(per_op);
        }
    });
    var final_result = tot.toFixed(2);
    $total.html(final_result)
   $('input[name="usertotal"]').val(final_result);
});
</script>

var per_op = $(this).attr('value');

var per_op = $(this).text();