The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 6.3055\\[1 em]x_2 &= -1.1528+1.0994i\\[1 em]x_3 &= -1.1528-1.0994i \end{aligned} $$Polynomial $ x^3-4x^2-12x-16 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.