we have two values of time and height
these could serve as our x and y
[tex]\begin{gathered} x_1=13,y_1=21.74_{} \\ x_2=16,y_2=22.58 \end{gathered}[/tex]to find the tree's growth rate, we find the slope.
[tex]=\frac{y_2-y_1}{x_{2-}x_{1_{}}}\text{ =}\frac{22.58\text{ - 21.74}}{16\text{ -13}}=\frac{0.84}{3}=\text{ 0.28 f}t\text{ /mo}[/tex]