If the point $(2,9)$ is on the graph of $y=f(x)$, then there is one point which must be on the graph of $y=f(-x)$. What is the sum of that point's coordinates?
I know that the graph of $y=f(-x)$ is the reflection of the graph of $y=f(x)$ across the $y$-axis. So, to find the point on $y=f(-x)$ that corresponds to $(2,9)$ on $y=f(x)$, I just need to change the sign of the $x$-coordinate. That means the point is $(-2,9)$. To find the sum of its coordinates, I just add the $x$- and $y$-values: $-2+9=7$. 