The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -0.3949\\[1 em]x_2 &= 2.6974+1.6894i\\[1 em]x_3 &= 2.6974-1.6894i \end{aligned} $$Polynomial $ x^3-5x^2+8x+4 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.