The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -6.1908\\[1 em]x_2 &= 1.5954+2.2821i\\[1 em]x_3 &= 1.5954-2.2821i \end{aligned} $$Polynomial $ -x^3-3x^2+12x-48 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.