The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.612\\[1 em]x_2 &= -2.306+7.3147i\\[1 em]x_3 &= -2.306-7.3147i \end{aligned} $$Polynomial $ x^3+4x^2+56x-36 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.