The problem is an exponential growth problem. The equation is Population = 11,000 times e0.018 x years
Our target is 26000. 26000/11000 = e0.018 x years This simplifies to 26/11 = e0.018 x years .
Take the natural log of both sides gives 3.2581 - 2.3979 = 0.018 x years.
Simplifies to 0.8692 = 0.018 x years. Divide both sides by 0.018 gives 47.79 or 48 years.