The solid shafts ABC and DEF and the gears shown are used to transmit 28 hp from the motor Mto a machine tool connected to shaft DEF. Knowing that the motor rotates at 280 rpm and that Tall = 3 ksi, determine the smallest permissible diameter of (a) shaft ABC, (b) shaft DEF. M 5.5 in. 2.5 in. 7.0 in. D B 4.0 in. F d (ABC) = d (DEF) = in. in.