The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.3588\\[1 em]x_2 &= -0.6175\\[1 em]x_3 &= 3.0087 \end{aligned} $$Polynomial $ 12x^3-33x^2-12x+8 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.