User defined function subtotal row.

Dear friends,

I have an excel file with header row of scrip name, buy qty, buy rate, buy total (buy qty * buy rate), sold qty, sold rate, sold total (sold qty * sold rate) and total (buy total - sold total). I am adding subtotals such that the subtotal is displayed at each change of scrip name for columns buy qty, buy total, sold qty and sold total. I would like to display average buy rate and sold rate as well, which are buy total / buy qty and sold total / sold qty respectively. How do I add those custom functions in the subtotal row?

Regards,
Pravin Kumar.

EXCEL_SUBTOTAL.jpg