The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -3.9322\\[1 em]x_2 &= 3.4661+1.8014i\\[1 em]x_3 &= 3.4661-1.8014i \end{aligned} $$Polynomial $ -x^3+3x^2+12x-60 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.