Financial Report Writing

Does anyone know how to add subtotals in the Financial Report Designer in Vantage -- what I need to do is to add a debit balance to a credit balance but have it ignore the debit and credit... Like 80,000 + -110,000 would be 190,000... I haven't created any other reports in Vantage's Financial Report Designer so I am fairly dumb in this area.
Thanks
Stephanie