The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 2.6106\\[1 em]x_2 &= -0.5553+0.917i\\[1 em]x_3 &= -0.5553-0.917i \end{aligned} $$Polynomial $ 4x^3-6x^2-7x-12 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.