Acountry's population in 1992 was 72 million. in 1998 it was 76 million. estimate the population in 2012 using the exponential growth formula. round your answer to the nearest million.

p=ae^kt

Your exponential growth formula, P(t) = A e^(kt), contains two unknown constants, A and k. Once you find them, you can find the population for any t. (I assume, t is measured in years.) From your "story", you have: 

72 million = P(1992) = A e^(1992 k) 
76 million = P(1998) = A e^(1998 k) 

From these two equations, you can find the two unknowns A and k (do it yourself). Once you do, your answer is 

P(2012) = A e^(2012 k)