How many will there be after 8 years?
When will we reach 3500 inhabitants?

A city has 2804 inhabitants. 
Five years later there are 2973 inhabitants.
We assume an exponential growth. 
Describe this as a function.

Let f(x) be an exponential function with starting value 
200 and a growth of 13% each year. 
Make the formula for the function.

How many years will it take to double the y-value? 

f(x) = (200 * 1.13^(x))
A = Intersect(f, a, (7.497205693236734, 500.0000000000007))
B = Intersect(f, b, (13.168622862016653, 1000.000000000001))
DoubleTime: x(B) - x(A)
c = 639 (slider from 100 to 5000, step 0.1)
d: y = c
e: y = (2 * c)
C = Intersect(f, d, (9.504251243654224, 638.9999999913234))
D = Intersect(f, e, (15.175668412434147, 1277.9999999826468))
NewDouble: x(D) - x(C)