The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -3.1562\\[1 em]x_2 &= -0.4219+2.4817i\\[1 em]x_3 &= -0.4219-2.4817i \end{aligned} $$Polynomial $ x^3+4x^2+9x+20 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.