The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 4.4537\\[1 em]x_2 &= -0.2269+1.4033i\\[1 em]x_3 &= -0.2269-1.4033i \end{aligned} $$Polynomial $ x^3-4x^2-9 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.