To solve this question, we will use the following formula for the average rate of change in the interval [a,b]:
![A=(f(b)-f(a))/(b-a).](https://img.qammunity.org/2023/formulas/mathematics/college/ghb6mj0zpeay48xci2548mvbhqma53nvvy.png)
From the given graph, we know that:
![\begin{gathered} f(6)\approx590, \\ f(0)=500. \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/5zz9yvdqf6lu6icp69rwvhg53mzso68pt8.png)
Therefore, the approximate rate of change of the first 6 years is:
![A=(590-500)/(6-0)=(90)/(6)=15.](https://img.qammunity.org/2023/formulas/mathematics/college/zbt8t6wjldvelltw9isz6t562gl1vboji3.png)
The closest answer from the options is $16.
Answer: $16.