The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -0.8132\\[1 em]x_2 &= -2.0934+4.4959i\\[1 em]x_3 &= -2.0934-4.4959i \end{aligned} $$Polynomial $ 4x^3+20x^2+112x+80 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.