A 7.5-ft-long solid steel shaft (G = 11.2 x 10^6 psi) is to transmit 15 hp at a speed of 1500 rpm. The shaft is limited to an allowable shearing stress of 4.5 ksi and an allowable angle of twist of 4 degrees. Determine:

a. The power transmitted by the steel shaft in units of in-lb/sec (Note: 1 hp = 33,000 ft-lb/min).
b. The corresponding torque for the steel shaft in units of in-lb.
c. The required diameter of the shaft (Show all units in your calculations).