What is the answer to POW 7 from IMP 4?

The answers are as followed:

The sum of the top cards from the card game invlolving 6 piles of cards and 5 extra cards is 31.

The way in which the entertainer knew this was that he used the equation

(13xP) -52 +X = Sum of top cards for the given situation.

Note: P = Number of piles, and X = Number of extra cards

Alternatively, you could use this formula:

(((((12+X)/2)-X)+7)P)- (52-X)