The initial population of a town is 127,866 and it grows with a doubling time of 18 years. what will the population be in 23 years?

The difference between 18 and 23 is 5, therefore 18/5= 3.6
From this, after the 18 years, the population will have doubled to 255732.
Then to find the increase, you will use 3.6 as  percent, and this will be 9206 people added in the population, therefore, making the total population 246938 after 23 years. 
Hope this helps