The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -1.6467\\[1 em]x_2 &= 30.3481\\[1 em]x_3 &= 1.1493+1.6375i\\[1 em]x_4 &= 1.1493-1.6375i \end{aligned} $$Polynomial $ x^4-31x^3+20x^2-200 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.