A fraction equals zero if and only if its numerator equals zero. So, you have
In turn, a product is zero if either of the factors is zero:
And we have
Those values are compatible with the existence of the fraction (i.e. they don't nullify the denominator), so we can accept them as zeroes.
part 1 answer = 8
part 2 answer = 72
part 1 explanation = add all of the numbers, then divide by how many numbers you have. so, 200/25 = 8.
part 2 explanation = not gonna lie, this is hard to explain, so just google how to do it.