Three concurrent forces, F1, F2 and F3, act on a block that is placed on a
horizontal surface. The resultant force on the block is 20.0 N at 0°. If F1 = 10.0 N
at 40° and F2 = 20.0 N at 180°, calculate the magnitude and direction of the force
F3. Sketch a vector diagram (not to scale) illustrating your solution.