The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 2.6344\\[1 em]x_2 &= 0.1828+1.733i\\[1 em]x_3 &= 0.1828-1.733i \end{aligned} $$Polynomial $ x^3-3x^2+4x-8 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.