To find the average population growth rate per year, you can use the following formula:
\[ \text{Average Growth Rate} = \frac{\text{Total Growth}}{\text{Number of Years}} \]
In this case, the total growth is 3,000 people and the number of years is 6.
\[ \text{Average Growth Rate} = \frac{3000}{6} = 500 \]
So, the town's average population growth rate is 500 people per year.