面积*（数量+价格+重量）=小计 怎么用jQuery实现

<script src="http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.7.2.min.js"></script>
<script>
    $(function () {
        $('#panel tr:even input').blur(function () {
            var total = 0, sum = 0,ipts;
            $('#panel tr:even').each(function () {
                ipts = $(this).closest('tr').find('input');
                var a = parseFloat(ipts.eq(0).val()) || 0, n = parseFloat(ipts.eq(1).val()) || 0, p = parseFloat(ipts.eq(2).val()) || 0, w = parseFloat(ipts.eq(3).val()) || 0;
                sum = a * (n + p + w);
                $(this).closest('tr').next().find('input').val(sum.toFixed(2));//保留2位小数
                total += sum;
            });
            $('#total').val(total.toFixed(2));
        });
    })
</script>
    总和：<input type="text" id="total" readonly="readonly" />
    <table id="panel">
        <tr>
            <td>面积：</td>
            <td><input id="area" type="text" class="price" value="16.2" /></td>
            <td>*(数量：</td>
            <td><input id="num" type="text" class="num" /></td>
            <td>+价格：</td>
            <td><input id="price" type="text" class="numm" /></td>
            <td>+重量：</td>
            <td><input id="weight" type="text" class="numm" />)</td>
        </tr>
        <tr>
            <td>小计：</td>
            <td><input id="subtotal" type="text" class="subtotal" /></td>
        </tr>
        <tr>
            <td>面积：</td>
            <td><input id="area" type="text" class="price" value="16.2" /></td>
            <td>*(数量：</td>
            <td><input id="num" type="text" class="num" /></td>
            <td>+价格：</td>
            <td><input id="price" type="text" class="numm" /></td>
            <td>+重量：</td>
            <td><input id="weight" type="text" class="numm" />)</td>
        </tr>
        <tr>
            <td>小计：</td>
            <td><input id="subtotal" type="text" class="subtotal" /></td>
        </tr>
    </table>