#### Answer

$x=2$

#### Work Step by Step

If the slope is undefined, we can surely state that the line is vertical.
The equation of a vertical line is always in the form of:
$x=a$, where $a$ is constant.
Here, the point given is $(2,4)$, which is on the line.
For this point, $x=2$ and this should be true for the other points on the line.
Thus, the equation of the line is:
$x=2$