problem: Given that $M( 1, -6)$ is the midpoint of $\overline{AB}$ and $A(-2, 1)$ is one endpoint, what is the sum of the coordinates of point $B$?
solution: Call the coordinates of point $B$ $(x,y)$. The coordinates of a midpoint are the average of the coordinates of the two endpoints, so we know that $\frac{-2+x}{2} = 1$ and $\frac{1+y}{2} = -6$. Solving for $x$ and $y$ gives $x = 4$ and $y = -13$. We take the sum of $x$ and $y$ for an answer of $\boxed{-9}$.