Answer
See below
Work Step by Step
They share the same y value at two points $(2,3)$ and $(-4,3)$. Because the axis of symmetry divides the parabola into mirror images, $(2,3)$ is the mirror image of $(-4,3)$ with respect to the mirror, and the two points are at the same distance from the mirror. Hence, the mirror is $x=\frac{2+(-4)}{2}=-1$
