The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.6767\\[1 em]x_2 &= -0.7786\\[1 em]x_3 &= -1.898 \end{aligned} $$Polynomial $ 3x^3+6x^2-x-3 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.