How to calculate Total based on Formula Value in xml publisher template

Hi,

I have issue ro create a formula to calculate Total. The calculate column is not direct xml tag field but formula column.

How can I do this?

Following is a example…

Let see order has 2 lines with qty, price, and discount. I am using following formula to get Line Amount. Both lines are in same group and using same this formula:

<?if:DISCOUNT_PCT = ''?><?(LINE_UNIT_SELLING_PRICE)* (LINE_QTY_ORDERED) ?><?end if?><?if:DISCOUNT_PCT !=''?><?((LINE_QTY_ORDERED*LINE_UNIT_SELLING_PRICE)-((LINE_QTY_ORDERED*LINE_UNIT_SELLING_PRICE)* (DISCOUNT_PCT*0.01)))?><?end if?>

                                                                                          Line Amount