Problem on Torsion/ratio of powers transmitted and angles of twist in equal lengths of these shafts

Problem on Torsion/ratio of powers transmitted and angles of twist in equal lengths of these shafts Problem :A solid shaft of 200 mm diameter has the same cross-sectional area as a hollow shaft of the same material with inside diameter of 150 mm. Find the ratio of (a) powers transmitted by both the shafts at the same angular velocity. (b) angles of twist in equal lengths of these shafts, when stressed to the same intensity.