Answer
$12$ teams per year.
Work Step by Step
The average rate of change of $f$ over the interval $[a, b]$ is given by:
Average rate of change of $f\displaystyle \ \ =\frac{f(b)-f(a)}{b-a}$
The units of the average rate of change of $f$ are units of $f(x)$ per unit of $x$.
Average rate of change of $f\ \ $ over $[2,6]$ is
$\displaystyle \frac{f(6)-f(2)}{6-2}=\frac{984-936}{4}=\frac{48}{4}=12$ teams per year.
