The axis of symmetry of a figure is the line that divides the figure into two parts that are equal to each other.
In the case of a parabola, as we have in the graph, the axis of symmetry is a vertical line that passes through the vertex.
The vertex of the parabola is at:
And the vertical line that passes through this point is:
This line is at x=3:
Thus, the equation of the axis of symmetry is:
Answer: