1. **Problem Statement:** Determine the axis of symmetry of the given graph. 2. **Understanding Axis of Symmetry:** The axis of symmetry of a graph, especially for parabolas, is a vertical line that divides the graph into two mirror images. 3. **Identifying the Axis of Symmetry:** From the graph, the axis of symmetry is the vertical line passing through the vertex of the parabola. 4. **Observation:** The vertex lies on the vertical line $x = 3$. 5. **Conclusion:** Therefore, the axis of symmetry is the line $$x = 3$$. This means the graph is symmetric about the vertical line $x=3$.