Answer:
x=4
Explanation:
Axis of symmetry is an invisible line that will divide the parabola in half, so if you were to fold it over itself, they will be on top of each other.
We can see that the bottom of the parabola is at x=4, so that will be the axis of symmetry. If we were to draw a line through x=4 (vertical line), we can see that it perfectly divides the parabola.
Hope this helps! :)