The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -4.1723\\[1 em]x_2 &= 0.0862+0.8436i\\[1 em]x_3 &= 0.0862-0.8436i \end{aligned} $$Polynomial $ x^3+4x^2+3 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.