ANSWER:
A. The average rate of change is about -72.4 thousand each year. The number of high school dropouts decreased by an average of about 72.4 thousand each year from 1978 to 2007.
Explanation:
We can calculate the average rate of change per year in the number of high school dropout, using the following formula:

We substitute the corresponding values and we calculate the average rate of change just like this:

Therefore, the correct answer is the following:
A. The average rate of change is about -72.4 thousand each year. The number of high school dropouts decreased by an average of about 72.4 thousand each year from 1978 to 2007.