Answer:
x = -4
Step-by-step explanation:
An undefined slope would look like a vertical line, up and down. This is shown using an x equals equation instead of a y equals equation.
Since the line goes vertically, you only need to look at the x-value to make the equation, since after doing x = -4 the line would keep going down until it touched (-4, -8).
The line would touch everything in the y-value but stay at x = -4.
Therefore the answer to this problem is x = -4. I've attached a picture (from desmos) showing what the graph of x = -4 would look like and how it touches the point (-4, -8).