Answer
$-513.29\ million/year$, see explanations.
Work Step by Step
Step 1. Recall the formula for the average rate of change $m=\frac{f(x_2)-f(x_1)}{x_2-x_1}$
Step 2. Based on the given conditions, we have $x_1=2006, f(x_1)=5302\ million$ and $x_2=2013, f(x_2)=1709\ million$
Step 3. Use the formula, we have $m=\frac{1709-5302}{2013-2006}\approx-513.29\ million/year$
Step 4. The above number means that the sales decreased at an average rate of $513.29\ million/year$ from 2006 to 2013.
