The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -0.7401\\[1 em]x_2 &= -2.63+1.0911i\\[1 em]x_3 &= -2.63-1.0911i \end{aligned} $$Polynomial $ x^3+6x^2+12x+6 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.