The masses of blocks A and B in Fig. 5.86 are 20.0 kg and 10.0 kg, respectively. The blocks are initially at rest on the floor and are connected by a mass less string passing over a mass less and frictionless pulley. An upward force F is applied to the pulley. Find the accelerations aA of block A and aB of block B when F is
(a) 124 N;
(b) 294 N;
(c) 424 N.