The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.3941\\[1 em]x_2 &= -0.6253\\[1 em]x_3 &= 16.2313 \end{aligned} $$Polynomial $ x^3-16x^2-4x+4 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.