เกี่ยวกับการแทรกตัวแปรลงไปในฟังชั่น ของ php ในส่วนของ Script ฟังชั่นครับ

<script>
		function fncSum()
	{
		 if(isNaN(document.frmMain.prod_price.value) || document.frmMain.prod_price.value == "")
		 {
			alert('(prod_price)Please input Number only.');
			document.frmMain.prod_price.focus();
			return;
		 }

		 if(isNaN(document.frmMain.quantity.value) || document.frmMain.quantity.value == "")
		 {
			alert('(quantity)Please input Number only.');
			document.frmMain.quantity.focus();
			return;
		 }

		 document.frmMain.sell_total.value = parseFloat(document.frmMain.price.value) * parseFloat(document.frmMain.quantity.value);
	}
	</script>
    <td width = "10%"><input type="text" name="prod_price<?php echo "$i";?>" size="8" OnChange="fncSum();"></td>
	<td width = "10%"><input type="text" name="quantity<?php echo "$i";?>" size="8"  OnChange="fncSum();"></td>
	<td width = "10%" align = "right"><input type="text" name="discount<?php echo "$i";?>" size="6" >%</td>
	<td width = "10%" align = "right"><input type="text" name="sell_total<?php echo "$i";?>" size="6" value = ""></td>