The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -3.0922\\[1 em]x_2 &= -0.7039+0.389i\\[1 em]x_3 &= -0.7039-0.389i \end{aligned} $$Polynomial $ 4x^3+18x^2+20x+8 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.