When talking about the rate of change on a line, we're talking about the slope.
Now, let's use points:
[tex]\begin{gathered} (4,-10) \\ \text{and} \\ (7,-30) \end{gathered}[/tex]
to estimate the slope of the line depicted in the graph.
(We'll get an aproximate value, since the graph is not suited for precise numerical calculations)
This way,
[tex]m=\frac{-30-(-10)}{7-4}\rightarrow m=\frac{-30+10}{3}\rightarrow m\approx-6.66[/tex]
The closest value to the slope we've calculated is:
F. -6.5°C/km
(Answer)
