Please answer:

@ Understanding Concepts 5. A construction worker uses a rope and pulley system to raise a 27-kg can of paint 3.1 m to the top of a scaffold (Figure 5). The downward force on the rope is 3.1 x 102 N as the rope is pulled 3.1 m. (a) Find the work done in raising the can of paint. (b) How much \"useful work" is done? (c) What is the efficiency of the rope and pulley in raising the can of paint? (d) Suggest why the efficiency of this simple machine is not 100%