If a population of rabbits, originally 15 000, is increasing at 3% per annum, find the population after 15 years have passed.
I would use the following population model. There are others you could consider
where P = population, = Initial Population, R = Growth Rate and t = time in years
In your case
= 15,000, R = 3% (increasing) and t = 15
you should be fine from here...
You have to think like if you where figuring out saving account interest.
15000 times 3% divide it by 100
45000 divide by 100 = 450
At the end of the first year you have 15450 rabbits. then 15450 is your new 100% and you start all over until 15 years have pass.
The exponential model is probably the simplest method.
Of course this is based on the assumption that the growth can be modelled by exponential growth and that there are no reasons for numbers to decline