ขอคำแนะนำครับ ต้องการผลบวก (แนวตั้ง) ของ field Labour ต้องเขียน code อย่างไรครับ

<?php


 $sql_show = "select * FROM customer";
	if($_POST['date_start']) {  
		$date_start = $_POST['date_start'];
		$date_stop = $_POST['date_stop']; 
		$sql_show .=" WHERE (reservation_date between '".$_POST['date_start']."' AND '".$_POST['date_stop']."') 
		
		ORDER BY reservation_date ASC";
   }

   $result_show = mysql_query($sql_show) or die(mysql_error());
	$chk_date = false;  
	$chk_sum = 0;
	$total = 0;
	while($rs = mysql_fetch_array($result_show)) {
		$id = $rs["id"];
		$reservation_date = $rs["reservation_date"]; 
		$date = '';
		$chk_total = '';
		
		if ($chk_date <> $reservation_date) {
			$date = $reservation_date;
			
			if ($chk_date <> false) {
				
		$chk_total = '<div class="total">'.number_format($chk_sum).'</div>';
	}
	$chk_sum = 0;
} 
      $edit_class = (trim($remark) == '') ? '' : ' hide';
		$tr_class = '';
		if ($level == '2') {
			$tr_class = ' class="tr2"';
		}
		else if ($level2 == '3') {
			$tr_class = ' class="tr3"';
		}
		echo '<tr align="center"'.$tr_class.'>';
		?>
        
        
        
<?php echo '<td height="42">'.$date.'</td>';?>

<td><?php echo $rs["fleet"];?></td>
<td><?php echo $rs["destination"];?></td>
<td><?php echo $rs["guest_name"];?></td>
<td><?php echo $rs["amount"];?></td>
<td><? $Labour = ($rs['amount']*15)/100; ?>
  <? echo $Labour; ?></td>

<td><strong><div class="<?php echo $rs["status"];?>"><p class="ex"><?php echo $rs["status"];?></p></div></strong></td>
<td><?php echo $remark;?></td>
<td>
<?php
if($rs["schedule1"] == "" or $rs["schedule2"] == ""){ // ถ้า schedule1 หรือ schedule2 ไม่มีค่า
    echo $rs["schedule1"].$rs["schedule2"];
}else{
    echo $rs["schedule1"]."<hr>".$rs["schedule2"];
}
?>
</td>
<td bgcolor="#999999">
	<div class="text-center<?php echo $edit_class;?>">
		<a href="edit.php?edit_id=<?php echo $id;?>">EDIT</a>
	</div>
</td>

<?php
echo '</tr>';
$chk_date = $reservation_date;
}
?>
<tr class="tr-last">
<td height="36"></td>
<td></td>
<td></td>
<td align="right">Total :</td>
<td align="center"><?php
$query = "SELECT SUM(amount) as s_Total FROM customer 
where reservation_date between '".$_POST['date_start']."' and '".$_POST['date_stop']."'
GROUP BY reservation_date between '".$_POST['date_start']."' and '".$_POST['date_stop']."'";  
$result = mysql_query($query) or die(mysql_error());
while($row = mysql_fetch_array($result)){
	echo number_format($row['s_Total']); 
	}?></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>

</table>