Sum in Report derived from an expression (1 Viewer)

I am trying to SUM the values for Profit in a report from a value derived using an expression. When try to create a Total, using Design Totals, Sum is greyed out.
Is there another way I can total these values. I have tried doing it in a Query but that was unsucessful.

I've never used Design Totals on report (never even noticed it was there). Just now looked at and Totals is greyed out. Oh, only available in Layout view. I seldom work with Layout view. Arithmetic functions only available if a number value is in the textbox. What is the expression generating value?