Answer
Decreasing
Work Step by Step
Average rate of change of $f\ \ $ over $[5,8]$ is
$\displaystyle \frac{f(8)-f(5)}{8-5}=\frac{1017-983}{3}=\frac{34}{3}=11\frac{1}{3}$ teams per year.
Average rate of change of $f\ \ $ over $[6,9]$ is
$\displaystyle \frac{f(9)-f(6)}{9-6}=\frac{1017-984}{3}=\frac{33}{3}=11$ teams per year.
Average rate of change of $f\ \ $ over $[7,10]$ is
$\displaystyle \frac{f(10)-f(7)}{10-7}=\frac{1010-982}{3}=\frac{28}{3}=9\frac{1}{3}$ teams per year.
We see that the 3-year average rates of change are DECREASING.
