Fields or report to calculate profit amount and percentage

I have a table called "Opportunity" and a table called "Expenses", an Opportunity can have many Expenses.  In the Opportunity table I have a field called "Current Year Fee".  In the Expense table there is a field called "Amount".  Since an Opportunity can have many Expenses and therefore many "Amounts", I am trying to create fields and or a report to calculate the difference or profit $ and % based on the "Current Year Fee" less all the expenses tied to that Opportunity.  I am still pretty new to QuickBase so I would really appreciate any help and the more details the better.  Thank you in advance!