$220$V$,50$ Hz$,4$ Pole, $3-$phase induction motor has the following parameter: maximum torque of $200\%$ at a slip $20\%,$ if the supply voltage is increased to $300$V at $60$ Hz$.$

a$)$ Obtain the change in the rotor current.

b$)$ The new maximum torque and slip at maximum torque.

c$)$ The change in the speed.

d$)$ The change in the starting torque.