The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 4.1098\\[1 em]x_2 &= -7.0101\\[1 em]x_3 &= 1.4502+0.3443i\\[1 em]x_4 &= 1.4502-0.3443i \end{aligned} $$Polynomial $ x^4-35x^2+90x-64 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.