#### Answer

6 and -3.

#### Work Step by Step

$ f'(x)$ exists for all x. Therefore, the only critical points are the solutions of $ fâ˛(x)=0$
$ f'(x)=3x^{2}-9x-54=0$
Or $ x^{2}-3x-18=0$
$\implies x= 6$ or $ x=-3$
Thus, the critical points are the roots $ c=6$ and $ c=-3$.