Here is a similar, but not identical example worked out for you, based on the folowing graph:
\begin{align*}
\text{Average rate of change of } f \text{ over } [1993, 1996] &= \frac{f(1996)-f(1993)}{1996 - 1993}\\
&= \frac{ 1.3 - 1.0 }{3} = 0.1
\end{align*}
Since this is positive, west coast exports to Asia were increasing at an average rate of 0.1 million containers per year over the period 1993-1996.
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