There are five boxes in a cargo hold. The weight of the first box is 200 kg and the weight of the second box is 20% more than the weight of the third box, whose weight is 25% more than the first box’s weight. The fourth box at t350 kg is 30% lighter than the fifth box. The difference in the average weight of the four heaviest boxes and the four lightest boxes is (a) 37.5 kg    (b) 51.5 kg    (c) 75 kg    (d) 112.5 kg