The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.2903\\[1 em]x_2 &= -0.5513\\[1 em]x_3 &= -3.6276\\[1 em]x_4 &= 6.8886 \end{aligned} $$Polynomial $ x^4-3x^3-26x^2-6x+4 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.