The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.3117\\[1 em]x_2 &= -0.6257\\[1 em]x_3 &= 2.564 \end{aligned} $$Polynomial $ 8x^3-18x^2-8x+4 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.