The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 5.6835\\[1 em]x_2 &= -8.8958\\[1 em]x_3 &= 13.2122 \end{aligned} $$Polynomial $ -x^3+10x^2+93x-668 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.