The roots of polynomial $ p(s) $ are:
$$ \begin{aligned}s_1 &= -3.7563\\[1 em]s_2 &= 0.8782+0.9089i\\[1 em]s_3 &= 0.8782-0.9089i \end{aligned} $$Polynomial $ -s^3-2s^2+5s-6 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.