Select option คำนวณ ให้ คูณ แบบ Apto ทำงัยครับผม

<?php
session_start();
require 'connect.php';

$action = isset($_GET['a']) ? $_GET['a'] : "";
$itemCount = isset($_SESSION['cart']) ? count($_SESSION['cart']) : 0;
if (isset($_SESSION['qty']))
{
    $meQty = 0;
    foreach ($_SESSION['qty'] as $meItem)
    {
        $meQty = $meQty + $meItem;
    }
} else
{
    $meQty = 0;
}
if (isset($_SESSION['cart']) and $itemCount > 0)
{
    $itemIds = "";
    foreach ($_SESSION['cart'] as $itemId)
    {
        $itemIds = $itemIds . $itemId . ",";
    }
    $inputItems = rtrim($itemIds, ",");
    $meSql = "SELECT * FROM childtb WHERE id in ({$inputItems})";
    $meQuery = mysql_query($meSql);
    $meCount = mysql_num_rows($meQuery);
} else
{
    $meCount = 0;
}
?>

<form action="updatecart.php" method="post" name="fromupdate">
					
                    <table width="100%" height="154" border="1" align="center" cellpadding="0" cellspacing="0" bordercolor="#C76A32" class="table-responsive";>
					  <center>
                        <tbody>
                          <tr>
                                <td width="150" height="50" bgcolor="#FD6600" align="center"></td>
                                <td width="120" height="50" bgcolor="#FD6600" align="center">ชื่อ</td>
                                <td width="200" height="50" bgcolor="#FD6600" align="center">รายละเอียด</td>
                                <td width="100" height="50" bgcolor="#FD6600" align="center">อุปการะต่อ/เดือน</td>
								<!--<td width="100" height="50" bgcolor="#FD6600" align="center">อุปการะ</td>-->
                                <td width="100" height="50" bgcolor="#FD6600" align="center">รวม</td>
                                <td width="100" height="50" bgcolor="#FD6600" align="center">ยกเลิกรายการ</td>
                          </tr>
                        </thead>
                        <tbody>
                            <?php
                            $total_price = 0;
                            $num = 0;
							
                            while ($meResult = mysql_fetch_assoc($meQuery))
                            {
                                $key = array_search($meResult['id'], $_SESSION['cart']);
                                $total_price = $total_price + ($meResult['product_price'] * $_SESSION ['qty'][$key]);
                                ?>
                                <tr>
                                    <td><img src="child_img/<?php echo $meResult['product_img_name']; ?>" border="0"></td>
                                    
                                    <td width="56" height="30" align="center"><?php echo $meResult['product_name']; ?></td>
                                    <td width="56" height="30" align="center"><?php echo $meResult['product_desc']; ?></td>
                                    <td width="56" height="30" align="center">
								    

								   
								   <select name="month" id="month"class="form-control"value="<?php echo $_SESSION['qty'][$key]; ?>" 
								   class="form-control" style="width: 60px;text-align: center;">
								  
								  <option value="1">1</option>
								  <option value="3">3</option>
								  <option value="6">6</option>
								  <option value="12">12</option>
								  
								  </select>
								  
								   
								   <input type="text" name="qty[<?php echo $num; ?>]"value="<?php echo $_SESSION['qty'][$key]; ?>" 
									
								   class="form-control" style="width: 60px;text-align: center;">
							      							
                                   <input type="hidden" name="arr_key_<?php echo $num; ?>" value="<?php echo $key; ?>">
								 
								 
                               </td>
							   
                               <!-- <td width="56" height="30" align="center"><?php echo number_format($meResult['product_price']); ?></td>-->
								
                                <td width="56" height="30" align="center">
								
					            <?php echo number_format(($meResult['product_price'] *  $_SESSION ['qty'][$key] )); ?></td>
                                    
								 
									
							    <td width="56" height="30" align="center"><a href="removecart.php?itemId=<?php echo $meResult['id']; ?>">
					            <span class="text-danger"><img src="img/delete.png"></span></a></td>
					
                   
                                
                                </tr>
								
                                <?php $num++; } ?>
								
                                <tr>
                                <td colspan="8" style="text-align: right;">
                                    <h4>จำนวนเงินรวมอุปการะทั้งหมด <?php echo number_format($total_price); ?> บาท</h4>
                                </td>
                            </tr>
                            <tr>
                                <td colspan="8" style="text-align: right;">
                                    <a href="order.php" type="button" class="btn btn-danger btn-lg" >ยืนยันทำรายการ</a>
                                </td>
                            </tr>
                        </tbody>
                    </table>
					
                   </form>
            <?php
			
            }
			
            ?>