Help need using sub report values in main report

Hi, I am new to crystal, and need some help on how to use a value from a sub report in the main report. I have seen the post on using shared variables and am able to pull the values over to the main report in a section under the sub report with the correct values using the shared variables. But I need to use 2 of these values to do a percentage calculation in the main report. When I create a new formula field in the main report to use these shared values from the sub reports that I pulled over I get a divide by zero error. Can anyone help?

Thanks