Answer:
This question is incomplete, i will answer it as:
"The initial population of a town is A, and it grows with a doubling time of 10 years. What will the population be in X years?"
Ok, the growth of a population usually is an exponential growth, so we can write this as:
P(t) = A*exp(r*t)
Where A is the initial population.
r is the rate of growth, and t is our variable, in this case, number of years.
Now we know that when t = 10y, the population doubles, so we should have:
P(10y) = 2*A = A*exp(r*10y)
2 = exp(r*10)
ln(2) = r*10
ln(2)/10 = r = 0.069.
Then our equation is:
P(t) = A*exp(0.069*t)
Now, if we want to know the population in X years, we need to replace the variable t by X
P(t = X) = A*exp(0.069*X)