I can think of two ways of interpreting this question.
First, consider simple growth, so the monthly rate would be 7.5%/12=0.625%. A formula would be P(n)=2000+(2000×0.625n)/100=2000+12.5n, where P(n) is the population after n months.
Second, consider compound growth. If r% is the monthly rate then the annual rate is (1+(r/100))¹²=1.075.
So 1+(r/100)=1.075^(1/12)=1.006045 approx. Therefore r=0.6045%, slightly less than the simple rate.
The expression for monthly increase in population where n=number of months is P(n)=2000(1.006045)ⁿ, where P is the population after n months.
(Putting n=12 gives us P(12)=2150 which is a 7.5% increase on 2000. Note that with r=0.625%, the annual increase would be approximately 7.5%. In fact it would be more like 7.76%.)