The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 1.2892\\[1 em]x_2 &= -1.7785\\[1 em]x_3 &= 3.4893 \end{aligned} $$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.