The roots of polynomial $ p(s) $ are:
$$ \begin{aligned}s_1 &= 1\\[1 em]s_2 &= -6 \end{aligned} $$The solutions of $ s^2+5s-6 = 0 $ are: $ s = -6 ~ \text{and} ~ s = 1$.
You can use step-by-step quadratic equation solver to see a detailed explanation on how to solve this quadratic equation.