รบกวนด้วยครับ : ต้องการผลรวมแนวคอลัมน์ ของค่าตัวเลข : PHP

<?php
	mysql_connect("localhost","root","root");
	mysql_select_db("db_computer");
	mysql_query("SET NAMES tis620");
	
?>
      <table width="30%" border="1" cellpadding="0" cellspacing="0">
           <tr>
             <td width="52%"><?php echo "Printer Name" ?></td>
             <td width="27%"><?php echo "Page of Print" ?></td>
             <td width="21%"><?php echo "Paper Usage" ?></td>
           </tr>
           
           <?php	
			  $SQL= "SELECT  prnID, prnName, pageprint, pageCopy, pageDuplex, 
							              SUM(pagePrint*pageCopy) AS pageOfPnt, 
							              SUM(ceil(pagePrint*pageCopy/pageDuplex)) AS paperUsage
								           FROM tb_prnreport
								                  GROUP BY prnName";
			 	 $res= mysql_query($SQL);
			      while ($row= mysql_fetch_assoc($res)) {
             ?>
                <tr">
			<?php
			echo "<td>".$row['prnName']."</td>
					<td>".$row['pageOfPnt']."</td>
					<td>".$row['paperUsage']."</td>";
			echo "</tr>";	
				}
		
			?>
                <tr>
                       <td>total : </td>
                       <td>xxx</td>
                       <td >yyy</td>
              </tr>
</table>