Blocks A, B, and C have weights of 50 lb, 25 lb, and 15 lb, respectively. Determine

Question:

Blocks A, B, and C have weights of 50 lb, 25 lb, and 15 lb, respectively. Determine the smallest horizontal force P that will cause impending motion. The coefficient of static friction between A and B is ?_s = 0.3, between B and C, ??_s = 0.4, and between block C and the ground ???_s = 0.35,