Problem on Torsion/Power Transmitted by hollow shaft/Diameter of Shaft/ Strength of Materials

Problem on Torsion/Power Transmitted by hollow shaft/Diameter of Shaft/ Strength of Materials Problem-A hollow shaft is to transmit 200 KW at 80 r.p.m. If the shear stress is not to exceed 60 MPa and internal diameter is 0.6 of the external diameter, find the diameters of the shaft.