Answer:
Option C. 4 years
Explanation:
Population growth of a town is described by the equation

where x is the number of years.
Now we have to calculate the duration after which population of the town will be 30000 with an average growth rate of 18%.
We will use the equation to get the value of x.


Now we take log on both the sides of the equation.
Log(1.94) = xlog(1.18)
0.2878 = .0719x

Therefore after 4 years population of the town will be 30000.