Assuming the growth is of 1st order, we can start using the formula for rate of 1st order reaction:
dN / dt = k * N
Rearranging,
dN / N = k dt
Where N = amount of sample, k = growth factor, t = time
Integrating the equation from N = Ni to Nf and t = ti to tf will result in:
ln (Nf / Ni) = k (tf – ti)
Finding for the growth factor k:
k = ln (Nf / Ni) / (tf – ti)
k = ln (1.022 Ni / Ni) / 1 year
k = 0.02176 / year
The population in 2011 is:
ln (Nf / Ni) = k (tf – ti)
ln (Nf / 25000) = (0.02176 / year) * (2011 – 2006)
Nf = 27,873.7 = 27,874