The 80-lb block is attached to link AB and rests on a moving belt. Knowing that µs = 0.25...

The 80-lb block is attached to link AB and rests on a moving belt. Knowing that µs = 0.25 and µk = 0.20, determine the magnitude of the horizontal force P that should be applied to the belt to maintain its motion (a) to the right, (b) to the left.