A drive shaft of a belt conveyor system transmits 12kW of power at a speed of 40 rpm. If the shaft diameter is 50mm * 120mm long, calculate a)The shear stress in the shaft.

b)The angle of twist if modulus of rigidity =80 GN/m2
c)If the shear stress is limited to 60 Mn/m2 what must the shaft diameter be increased to.
Any help with this question would be very helpful