The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -0.8751\\[1 em]x_2 &= 2.9376+0.7157i\\[1 em]x_3 &= 2.9376-0.7157i \end{aligned} $$Polynomial $ x^3-5x^2+4x+8 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.