The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.546\\[1 em]x_2 &= -1.523+1.1591i\\[1 em]x_3 &= -1.523-1.1591i \end{aligned} $$Polynomial $ 2x^3+5x^2+4x-4 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.