I am new to crystal and I feel like this should be easy but my username should say it all…

I have a report(not created by me) that has a formula that calculates per inventory item the following.

Quantity on Hand + Quantity in Production = x then subtracts quantity on order. I am looking to filter my report to only show me the shortages so anything that formula returns a value of <0 I want to see.

The selection expert does not allow me to filter based on a formula field in the report..