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 (see the X-ray image in figure A). 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 311 N is applied to the leg as depicted in figure B to realign the parts of the femur, how much mass m must be attached to the bottom pulley?

____kg