The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -0.542\\[1 em]x_2 &= -3.3212\\[1 em]x_3 &= 0.2649+0.4204i\\[1 em]x_4 &= 0.2649-0.4204i \end{aligned} $$Polynomial $ 9x^4+30x^3+4 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.