8–138. The uniform 60-kg crate C rests uniformly on a 10-kg dolly D . If the front casters of the dolly at A are locked to prevent rolling while the casters at B are free to roll, determine the maximum force P that may be applied without causing motion of the crate. The coefficient of static friction between the casters and the floor is μ_f=0.35 and between the dolly and the crateμ_d=0.5 .