Solve the all parts of given question:
Question: You are lowering two boxes, one on top of the other, down the ramp by pulling on a rope parallel to the surface of the ramp. Both boxes move together at a constant speed of 15.0 cm/s. The coefficient of kinetic friction between the ramp and the lower box is .420 and the coefficient of static friction between the two boxes is 0.756. The top box mass is 32.0 kg and the bottom box is 48.0 kg. (The ramp's length is 4.75m and the height of the ramp is 2.50m).
Part A: What force do you need to exert to accomplish this?
Part B: What is the magnitude of the friction force on the upper box?
Part C: What is the directing of the friction force on the upper box?
I need help to compute the directing of the friction force on the upper box.