The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 1.7282\\[1 em]x_2 &= -0.3641+3.0209i\\[1 em]x_3 &= -0.3641-3.0209i \end{aligned} $$Polynomial $ x^3-x^2+8x-16 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.