The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 2.5249\\[1 em]x_2 &= -6.4244\\[1 em]x_3 &= 3.4244\\[1 em]x_4 &= -7.5249 \end{aligned} $$Polynomial $ x^4+8x^3-26x^2-167x+418 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.