selection formula

I am kind of new to crystal reports and I am using visual studio 2002. What I need to do is select all records from a table excluding records where the difference between two fields (costa - costb) is less than 100, but only when a third field (code) contains code 'D'. Is that something that can be done using the select wizard? Maybe this is less complicated than I think?

on selection expert choose fromula editor set formula something like:
if ({costa} -Cost{b}) < 100 and {Code} < 'D'