Answer
$-1.6$ births per thousand per year, see explanations.
Work Step by Step
Step 1. Identify the needed data: $x_1=1991, f(x_1)=61.8$ and $x_2=2013, f(x_2)=26.6$
Step 2. Use the formula for the average rate of change: $m=\frac{f(x_2)-f(x_1)}{x_2-x_1}$, we have $m=\frac{26.6-61.8}{2013-1991}\approx-1.6$ births per thousand per year. This means that the number of births per thousand for adolescent females decreased at a rate of 1.6 births per thousand per year during this time.
