The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -0.6666+0.9351i\\[1 em]x_2 &= -0.6666-0.9351i\\[1 em]x_3 &= 1.9166+0.3439i\\[1 em]x_4 &= 1.9166-0.3439i \end{aligned} $$Polynomial $ 2x^4-5x^3+10 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.