The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 1.3593\\[1 em]x_2 &= -1.1797+0.903i\\[1 em]x_3 &= -1.1797-0.903i \end{aligned} $$Polynomial $ 3x^3+3x^2-3x-9 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.