assuming exponential growth, we have

where is the population after time , is the initial population, is the rate of growth, and is time

since it grows from 81,500 to 103,200 over a 7 year period, we have:

solve that for , that will give you the rate of growth.

then use it to find what they asked you for, which would be to solve:

for (you will know the value of at this point, the value of is immaterial)