At a construction site, a 67.0 kg bucket of concrete hangs from a light (but strong) cable that passes over a light friction-free pulley and is connected to an 85.0 kg box on a horizontal roof (see the figure ). The cable pulls horizontally on the box, and a 50.0 kg bag of gravel rests on top of the box. The coefficients of friction between the box and roof are shown(µs=0.700, µk=0.400). The system is not moving. Find the friction force on the bag of gravel. Find the Friction force on the box.