The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.784\\[1 em]x_2 &= -2.336\\[1 em]x_3 &= 6.552 \end{aligned} $$Polynomial $ x^3-5x^2-12x+12 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.