4. (20 points) The 60-mm diameter A-36 steel shaft is subjected to a 5 kN m/m uniform distributed torque along section AB and a 2 kN m concentrated torque at end A. Determine the angle of twist of end A with respect to fixed end C. Take Gst = 75 GPa. C 400 mm B 600 mm A 5 kN m/m 2 kN·m