#### Answer

$x$

#### Work Step by Step

RECALL:
A vertical line has an equation in the form $x=h$ where $h$ is a real number.
All points on the line have an x-coordinate of $h$.
The given vertical line contains the point $(-4, 8)$.
The x-coordinate of this point is $-4$.
Thus, the equation of the vertical line is $x=-4$.
Therefore, the missing expression in the given statement is:
$x$