The roots of polynomial $ p(m) $ are:
$$ \begin{aligned}m_1 &= 1\\[1 em]m_2 &= -2 \end{aligned} $$The solutions of $ m^2+m-2 = 0 $ are: $ m = -2 ~ \text{and} ~ m = 1$.
You can use step-by-step quadratic equation solver to see a detailed explanation on how to solve this quadratic equation.