Three Blocks, Light Connecting Ropes, and a Light Frictionless Pulley

Short Answer

Three blocks, light connecting ropes, and a light frictionless pulley comprise a system, as shown in the figure. An external force of magnitude P is applied downward on block A, causing block A to accelerate downward at a constant 2.5 m/s². The tension in the rope connecting block B and block C is equal to 60 N.
(a) What is the magnitude of the force P?
(b) What is the mass of block C?