The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -0.1538\\[1 em]x_2 &= 1.2603\\[1 em]x_3 &= -3.4398 \end{aligned} $$Polynomial $ 3x^3+7x^2-12x-2 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.