Answer: C: Exam>=90
Explanation:
The flaw you did was divided it by two, but you have to divide it by the number of numbers you have, which would be 4. that would give you 75, and then you have to figure out what score you would need to get on two tests (The question says it counts as 2 tests) which ends up being 90% to give you an 80%. So the answer is C! I hope this helps :)