We have that if we assume standard exponential growth, the equation of the population will be:
if we start counting from the moment that the population was 7000. We are given that 7000* 
=12000, namely that P(5)=12000 and we need to find 
. Since e^(10k)=e^(5k)*e^(5k), and since we can solve for e^(5k) from P(5), we have:
e^(5k)=12000/7000 and we can calculate P(10). P(10)=7000
= 20571 people.
e^(5k)=12000/7000 and we can calculate P(10). P(10)=7000