The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -0.4023\\[1 em]x_2 &= 0.2012+0.8877i\\[1 em]x_3 &= 0.2012-0.8877i \end{aligned} $$Polynomial $ 3x^3+2x+1 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.