The hollow shaft provided to the right has an inner diameter of 4.5 in and an outer diameter of 8.5 in. The shaft material has an allowable shear stress of 12 ksi. d 4.5 in do-8.5 in a) Determine the maximum torque (in units of lb-ft) that can be applied to the shaft. b) How much power can be delivered if the shaft is rotating 20 revolutions per second? Express in units of horsepower (hp). 1 hp = 550 lb-ft/s.