7. Three forces try to rotate a solid disc around its central axis "O". For a = 80 cm, b = 120 cm, 0 = 15, |F = 30 N, F2 = 40 N, and |F3|= 25 N. (a) Find the moment arm for each of these forces. (b) Determine the magnitude and direc- tion of torque that each force exert on the wheel. (c) Find (both the magnitude and the di- rection of) the net torque on the wheel. F b a F3 0 F2