The function $\bm{f}(\bm{x})=\frac{1}{9}(x-7)^{2}+3$ gives a metal ball's height above the ground $\bm{f}(\bm{x})$, in inches, $\bm{x}$ seconds after it started moving on a track, where $0\leq\bm{x}\leq 10$. Which of the following is the best interpretation of the vertex of the graph of $\bm{y}=\bm{f}(\bm{x})$ in the $xy$-plane?