Let be the undirected binary tree from problem $3\mathrm{.}1.$ For each pair of vertices, we can compute the distance between these vertices. In the binary tree above, for example, we have dist$($d$,$i$)=5$ and dist$($l$,$o$)=6.$

We define the diameter of T to be the maximum$$ value of $,$ chosen over all pairs of vertices x and y in T

Clearly explain why the diameter of the above tree is $7.$