A 440 V, 50 Hz, 4-pole 3-phase, delta-connected motor has a leakage impedance of (0.3 + j 5.5 + 0.25/s) \Omega /phase (delta phase) referred to the stator. The stator to rotor voltage ratio is 2.5. Determine the external resistance to be inserted in each star phase of the rotor winding such that the motor develops a gross torque of 150 Nm at a speed of 1250 rpm.