The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 4.6384\\[1 em]x_2 &= -13.0982\\[1 em]x_3 &= 16.4598 \end{aligned} $$Polynomial $ x^3-8x^2-200x+1000 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.