Issue on Setting Up Query

Dear Experts

I am confused on setting up a query.

The scenario is as follow:

I have setup 3 UDFs in the title level of Marketing Document (Sales Order) and named it as Cost1, Cost2 and Gross Profit.

I would like a query that could calculate the Gross Profit by assigning a formatted search using the Document Total minus Cost1 minus Cost2 given that the result would change if any of the variables in the formula changes.

Any good suggestions?

Thank you

Regards

Elton