The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -0.4746\\[1 em]x_2 &= -1.3691\\[1 em]x_3 &= -6.1563 \end{aligned} $$Polynomial $ x^3+8x^2+12x+4 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.