The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -0.5348\\[1 em]x_2 &= 1.3924+1.3419i\\[1 em]x_3 &= 1.3924-1.3419i \end{aligned} $$Polynomial $ -4x^3+9x^2-9x-8 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.