The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.1461\\[1 em]x_2 &= -0.2925\\[1 em]x_3 &= 0.6732+1.3735i\\[1 em]x_4 &= 0.6732-1.3735i \end{aligned} $$Polynomial $ 10x^4-12x^3+21x^2+4x-1 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.