The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.8329\\[1 em]x_2 &= -2.3776\\[1 em]x_3 &= 4.5446 \end{aligned} $$Polynomial $ x^3-3x^2-9x+9 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.