The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -0.4691\\[1 em]x_2 &= 1.3264\\[1 em]x_3 &= -1.6073 \end{aligned} $$Polynomial $ 4x^3+3x^2-8x-4 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.