The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.6906\\[1 em]x_2 &= -1.5223\\[1 em]x_3 &= -0.2508+0.7558i\\[1 em]x_4 &= -0.2508-0.7558i \end{aligned} $$Polynomial $ 3x^4+4x^3-2 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.