The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 3.6337\\[1 em]x_2 &= -0.3168+1.7894i\\[1 em]x_3 &= -0.3168-1.7894i \end{aligned} $$Polynomial $ x^3-3x^2+x-12 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.