The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -3.1046\\[1 em]x_2 &= 0.5523+0.3527i\\[1 em]x_3 &= 0.5523-0.3527i \end{aligned} $$Polynomial $ 3x^3+6x^2-9x+4 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.