The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.8794\\[1 em]x_2 &= -1.3473\\[1 em]x_3 &= -2.5321 \end{aligned} $$Polynomial $ x^3+3x^2-3 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.