The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -1.5719\\[1 em]x_2 &= -10.6141\\[1 em]x_3 &= 13.186 \end{aligned} $$Polynomial $ x^3-x^2-144x-220 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.