The starting population of the town is 24,721 and it's population growth rate is -2.9% per year (negative because it's declining, not growing).
Since the town loses 2.9% of its population per year, find what 2.9% of the town is and then multiply it by 12. Subtract that from the starting population to get your final answer.
So...
24,721 × 2.9% = 716.909 ≈ 717 people per year
717 × 12 = 8,604
24,721 - 8,604 = 16,117
Answer: a. 16,118