Do you mean the following?
. . . . .y = 3x<sup>2/3</sup> - x<sup>2</sup>
If so, just use the Power Rule:
. . . . .For y = ax<sup>n</sup>, y' is given by y' = anx<sup>n-1</sup>.
If you get stuck, please reply showing what you have tried.
Thank you.
Eliz.