The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -3.3553\\[1 em]x_2 &= 0.1777+1.0773i\\[1 em]x_3 &= 0.1777-1.0773i \end{aligned} $$Polynomial $ x^3+3x^2+4 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.