[tex]\begin{gathered} \text{average rate of change of f(t) = }\frac{\Delta f}{\Delta t}=\frac{f(2)-f(0)}{2-0} \\ \text{From your question, I inferred that:} \\ f(2)\text{ = 36f}eet\text{ per second, and f(0) = 18f}eet\text{ per second} \\ \Rightarrow\text{ average rate of change of f(t) = }\frac{36-18}{2-0}=\frac{18}{2}=9fts^{-2} \end{gathered}[/tex]
