To calculate the percent increase in the population from 2012 to 2017, you can use the following formula for percent increase:
\[ \text{Percent Increase} = \left( \frac{\text{New Value} - \text{Old Value}}{\text{Old Value}} \right) \times 100 \]
In this case, the old value (2012 population) is 8,000, and the new value (2017 population) is 11,400.
Now, substitute the values into the formula:
\[ \text{Percent Increase} = \left( \frac{11,400 - 8,000}{8,000} \right) \times 100 \]
First, calculate the difference in population:
\[ 11,400 - 8,000 = 3,400 \]
Now, substitute this value back into the formula:
\[ \text{Percent Increase} = \left( \frac{3,400}{8,000} \right) \times 100 \]
Now, divide \(3,400\) by \(8,000\):
\[ \frac{3,400}{8,000} = 0.425 \]
Finally, multiply by 100 to get the percentage:
\[ 0.425 \times 100 = 42.5 \]
Therefore, the percent increase in the population from 2012 to 2017 was \( \boxed{42.5%} \).