The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -0.3607\\[1 em]x_2 &= -1.1439\\[1 em]x_3 &= -9.6954 \end{aligned} $$Polynomial $ 5x^3+56x^2+75x+20 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.