I think you'd need to creates fields that gives you the sum for a particular category SUM(IIF([Category]='General,[Your Measure],0)) then create another field where you divide the sum of one cat by the other.
The topic question is rather old, anyway...
Actually, what Ivan Young has been suggested could lead to the solution.
Definitely, not the solution (the only one), as we would usually find
with Tableau there are multiple paths to the final destination available.
Following Ivan's path, one could build the calculations (as in the attached).
So could you, too.
sample_YF.twbx 308.5 KB