A 3-phase, 50 Hz, 4-pole, 400 V, wound rotor induction motor has a D-connected stator winding and Y-connected rotor winding. There are 80% as many rotor conductors as stator conductors. For a speed of 1425 rpm, calculate
(a) the slip,
(b) the rotor induced emf between the two slip rings, and
(c) the rotor frequency