A wheel-and-axle system shown consists of two coaxial wheels of radius r = 2 meters and R = 6 meters. The forces applied to the system as shown in the diagram are:
F1 = 80 N
F2 = 80 N
F3 = 40 N
F4 = 30 N
If counterclockwise is positive, what is the net torque on this system?