The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -1.2134\\[1 em]x_2 &= 0.6067+1.4506i\\[1 em]x_3 &= 0.6067-1.4506i \end{aligned} $$Polynomial $ x^3+x+3 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.