I have tried writing this many ways and I'm not getting a good formula....  Can anyone help?

I need:

If "Method_Field" (which is radio button for 3 options, user must select 1) is "Ad"

Then the # of attendees from the RCC-Staff + Law_Enforcement + Legal_System_Prof + Healthcare_Prof  + Social_Services + Educational_ Prof + DV_Prof + Disabilities_Specialists + College_University + Multidisciplinary fields

Resulting in a cumulative total number of attendees from the training, where the ad was placed in the conference welcome packet = Ad Outreach.