4.57 Two boxes, A and B, are connected to each end of a light vertical rope, as shown in Fig. P4.57. A constant upward force F =80.0 N is applied

to box A. Starting from rest,box B descends 12.0 m in 4.00 s. The tension in the rope connecting the two boxes is 36.0 N.|(a) What is the mass of box B? (b) What is the mass of box A?