The graph illustrates the height of the tree over time. The rate of the tree's growth is going to be the change in height over a given time interval, which graphically, is the slope of the line. So simply find the slope of the given line to find the growth rate of the tree. If you look at the years from 0 to 2, the height changes from 0 to 5. So the tree grew 5/2 or 2.5 inches per year.
