PHYSICS HELP!!! pulleys, etc?

In traction... When a large bone such as the femur is broken, the two pieces are often pulled out of alignment by the complicated combination of tension and compression forces that arise from the muscles and tendons in the leg. To realign the bones and allow proper healing, these forces must be compensated for. A method called traction is often employed. If a total tension force of 400 N is applied to the leg to realign parts of the femur, how much m m must be attached to the bottom pulley?