The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -3.3032\\[1 em]x_2 &= -58.3484+20.2483i\\[1 em]x_3 &= -58.3484-20.2483i \end{aligned} $$Polynomial $ x^3+120x^2+4200x+12600 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.