Hints to Calculate the Unknown Mass
1. Once you know the gravitational force acting on the block, the applied force (Tension) is the only variable that is not predetermined (because you have already determined). Solve for the applied force.
2. If you know the gravitational force, then you can break it into its components: along the incline and into the incline. From this we can find the normal force. From that, with known, we can find the frictional force. The only unknown left is the applied force (Tension). Solve for the applied force. How much weight must be placed on the hanger?