A 20 mm diameter shaft with a 6 mm diameter transverse hole is made of cold-drawn steel having Ultimate strength = 550 MPa and Yield strength = 462 MPa. Surfaces in the vicinity of the hole have a machined finish. Estimate the Safety Factor with respect to infinite fatigue life for
(a) a torque fluctuating between 0 and 100 N.m,
(b) a completely reversed torque of 50 N.m, and (c) a mean torque of 60 N.m plus a superimposed alternating torque of 40 N.m.