The force P is applied to the 175-lb block when it is at rest. Determine the magnitude and direction of the friction force exerted by the surface on the block if (a) P = 0, (b) P = 70 lb, and (c) P = 108 lb. (d) What value of P is required to initiate motion up the incline? The static and kinetic coefficients of friction between the block and the incline are μs = 0.26 and μk = 0.20, respectively. The friction force is positive if up the incline, negative if down the incline.