the maximum point is 150 (6*25)

He got

that is

so he had somehow minus 94 points from the maximum.

Each wrong answer gives you minus 8 points from the maximum points.

(-6 for not getting it correct and the minus 2 for answering wrong).

So the question is now.

How many questions can go wrong and still get 56 points?

The answer is

so 12 questions can go wrong and u can still get 56 points.

That leaves you with 25-12 = 13

Understandable?

Regards Henry