A $4-$pole, $20KW,50Hz,400V$ squirrel cage induction motor has a starting torque of $16007$ Nm and full load torque of $120$ Nm calculate

$($i$)$ Starting torque for a stator voltage of $300$ V $.$

$($ii$)$ Voltage so that mutor operates satisfactorly at full load from a $60$ Hz source.

$($iii$)$ Voltage applied io stator so that full load torque is developed at starting.