A compound shaft is made of an aluminium rod, 40 mm diameter, and 1 m long, and a steel rod, 20 mm diameter, and 1.5 m long. If the maximum permissible shear stresses in aluminium and steel are 40 MPa and 90 MPa, and G is 28 GPa and 85 GPa, respectively, find the maximum torque that can be applied as shown. Also find the angle of twist between A and B.