The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -3.227\\[1 em]x_2 &= 0.1135+0.4686i\\[1 em]x_3 &= 0.1135-0.4686i \end{aligned} $$Polynomial $ 4x^3+12x^2-2x+3 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.