The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.1746\\[1 em]x_2 &= -0.3921\\[1 em]x_3 &= 1.2176 \end{aligned} $$Polynomial $ 12x^3-12x^2-4x+1 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.