A shaft with a 2-inch outer diameter must deliver 5000 ft-lbs of torque. The shaft must be hollow and must simultaneously carry hydraulic fluid at an internal pressure of 30,000 psi. Assuming the shaft is closed-ended, and using the von Mises yield criterion with a safety factor of 1.2, specify the maximum inner diameter for the shaft for a yield strength of (a) 93.6 ksi and (b) 81.6 ksi. State whether the most severe state of stress occurs on the inner or outer surface in each case.