The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 3.3961\\[1 em]x_2 &= -1.6981+0.8063i\\[1 em]x_3 &= -1.6981-0.8063i \end{aligned} $$Polynomial $ x^3-8x-12 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.