It doesn't give the entire question, Do they want to know how many pieces were in the total cake? If so, I think it would be 384. You subtract the 3 pieces that Mindy ate and that leaves 96 that Tony had which was supposed to be 1/4 of the cake. Dividing the cake into 4 sections of 96 and multiplying would give you 384.
If they want to know how many slices of cake were left after Tony ate the fourth (96 slices), it would be 288
translates to 
