6.25 A three-phase, six-pole, 150 hp, 380V, 50Hz, wye-connected induction motor has the following constants in ohms per phase referred to the stator:
R R 1 = Ω 0 0. 9 2 = Ω 0 0. 7
X1 = Ω 0.195 X2 = Ω 0.172
Xm = Ω 6 8. 3

Determine the following:
(a) The slip at which the maximum torque is developed
(b) The speed at which the maximum torque is developed
(c) The maximum torque developed
(d) The starting torque developed
(e) The speed at which the maximum torque is doubled, if the rotor resistance is doubled
(f) The maximum torque developed, if the rotor resistance is doubled
(g) The starting torque developed, if the rotor resistance is doubled