The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -0.3102\\[1 em]x_2 &= 2.6248\\[1 em]x_3 &= 0.8427+2.0501i\\[1 em]x_4 &= 0.8427-2.0501i \end{aligned} $$Polynomial $ x^4-4x^3+8x^2-10x-4 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.