The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 3.3146\\[1 em]x_2 &= 0.8427+1.3052i\\[1 em]x_3 &= 0.8427-1.3052i \end{aligned} $$Polynomial $ -x^3+5x^2-8x+8 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.