Part A. the answer is 7 because in 6 months Matthew will have $225 and if you add 30 you get $255.
Part B. It's the answer because its the only one that makes sense. 250 = 450 + 30. Its 45 not 450. 250 = 30.2 + 45. It's 30 not 30.2 and 30 30 well 30 30 doesn't make sense either.