The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -0.753\\[1 em]x_2 &= 3.6265\\[1 em]x_3 &= 5.1266 \end{aligned} $$Polynomial $ -x^3+8x^2-12x-14 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.