点击Cart.php中的“继续”，我需要在Cart.php的ajax_cart.php中显示一个值“$ tot”

Question

Cart.php： 从Cart.php调用ajax_cart的ajax代码显示总金额计算的值。单击继续后，我需要在同一页面中显示值..

ajax code

function gettotal(){
            $.ajax({
                type: "POST",
                url: 'ajax_cart_total.php',
                data: {action: 'call'},
                success: function(html){
                    alert html;
                }
                });
        }


html
*****
<a class="btn btn-default check_out" href="" onClick="gettotal()">Continue</a>
<li>Total <span id="disp2"></span></li> // value from ajax_cart should be displayed here..

ajax_cart.php： 所需的值取自表格并计算得出总金额

<?php
@mysql_connect("localhost","root","");
mysql_select_db("onlineshopping");
session_start();
$s=$_SESSION['USER']['ID'];
if($_POST['action']=='call'){
$c=mysql_query("select * from totcalcu where USER_ID='$s'");
$cr=mysql_fetch_array($c);
$subt=$cr['SUBTOTAL'];
$tax=$cr['TAX'];
$ship=$cr['SHIPPING_COST'];
$tot=$subt+$tax+$ship; // calculation of total done
    ?>
<span id="disp2"><?php echo $tot; ?></span>
<?php 
$ins=mysql_query("update totcalcu set TOTAL='$tot' where USER_ID='$s'");
}
?>

我无法更改HTML代码..请帮忙