The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -3.3286\\[1 em]x_2 &= 2.1643+0.8507i\\[1 em]x_3 &= 2.1643-0.8507i \end{aligned} $$Polynomial $ x^3-x^2-9x+18 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.