The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -2.1746\\[1 em]x_2 &= 0.0873+1.1713i\\[1 em]x_3 &= 0.0873-1.1713i \end{aligned} $$Polynomial $ x^3+2x^2+x+3 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.