The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 2.4969\\[1 em]x_2 &= -0.0401+0.4457i\\[1 em]x_3 &= -0.0401-0.4457i \end{aligned} $$Polynomial $ 12x^3-29x^2-6 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.