Question

The bird population on an island is declining at a rate of 4% per year. The population was 2700 in the year 2015.

Answer 1

You just follow the formula and see what it gets you from there.
The formula itself is literally b(1-r)t.
b= 2700
1 - 4% = .96
t = 5 years from 2015
This is a prediction, so it's exact value is irrelevant as long as it is close to your options, which Option C, 2202, is the best option for this.
I didn't follow the formula, however. I just did 10% of 2700, which is 270, and just multiplied it by 2, to get 20% of 2700 (Which is equal to 4% for five years decrease) and just subtracted the difference, leaving me with 2160, which is closer to 2202 rather than 2035. [Using the formula in the calculator kinda confused me, as it didn't turn out so pretty.]