The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 2.8314\\[1 em]x_2 &= -19.4157+11.7464i\\[1 em]x_3 &= -19.4157-11.7464i \end{aligned} $$Polynomial $ x^3+36x^2+405x-1458 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.