DataSource Controls :: Subtracting One Column Total From Another?

Customers of hours buy packs of hours, these are credited and debited on their account. We have a prepayhours table and that has various columns in it, one credit and one debit. I have written a query using the Query building and SQLDS to total these columns, which is fine. What i really want to do is get that query, or if there is an easier way to add up all the debits and subtract them from the total of credits so you would end up with a + or - totalThen with that i can put it into a label or if there was a way to add a row at the end of my gridview which just said total in one column and the total of the hours in the next.

I have some SQL code which seems to work in SQL 2008 but not in the SQL designer for VWD.

CREATE VIEW dbo.prepayhrstotals
AS
SELECT COUNT(Debit) AS cntDebit, COUNT(Credit) AS cntCredit
FROM prepayhrs
GO
SELECT (cntdebit - cntcredit) AS totalhours
FROM prepayhrstotals