Physics education research, electronic materials, and the musings of Christopher Moore, Ph.D.

For a serious fractures of the leg, the leg may need to have a stretching force applied to it to keep contracting leg muscles from forcing the broken bones together too hard. This is often done using traction, an arrangement of a rope, a weight, and pulleys as shown in the figure above. The rope must make the same angel on both sides of the pulleys so that the net force of the rope on the pulley is horizontally to the right, but θ can be adjusted to control the amount of traction. The doctor has specified 50 N of traction with a 4.2 kg hanging mass. What is the proper angle θ?

I found a picture that matches the figure but it has the wrong numbers. The numbers are given in the problem.
Here is the link to the picture  http://www.webassign.net/knight/p5-33alt.gif

This one is pretty hard. Let's see if any of you can figure it out. 
(note: Please show work)