A tubular aluminum bar (G = 4 ( 106 psi) of square cross section (see figure) with

Question:

A tubular aluminum bar (G = 4 ( 106 psi) of square cross section (see figure) with outer dimensions 2 in. ( 2 in. must resist a torque T = 3000 lb-in.
Calculate the minimum required wall thickness tmin if the allowable shear stress is 4500 psi and the allowable rate of twist is 0.01 rad/ft.