Answer:
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A) 13 students
b) 13 students
c) 37 students
You can't change the sum by changing the grouping. Any way you cut it, you will always get 226, as you only have addition operations, and the commutative property [a+(b+c)=(a+b)+c] means that the sum will always be the same.
If they have -8 points and +6 points, that'd leave them with a total of -2 points.
So the answer is -2.