The Problem:

The number of flu viruses in Jake's body is growing exponentially.
At noon ( t = 0 ), the number of flu viruses in Jake's body was one million.
At 2 PM ( t = 2 ), the number of viruses in Jake's body was 2 million.
How many flu viruses will inhabit Jake's body at 6 PM ( t = 6 )?

The solution:

Let Q(t) equal the number of flu viruses in Jake's body t hours after noon.
Exponential growth of Q(t) implies that Q(t) = Qo ekt
Substituting t = 0 , we find (1 million) = Qo ek(0) = Qo(1) = Qo
Thus, for any t, Q(t) = (1 million) ekt
Substituting t = 2 , we find (2 million) = (1 million) ek(2),
        and thus ek(2) = 2
We could now find the value of "k", but this is unnecessary
We seek Q(t) at 6 PM ( t = 6 )
Substituting t = 6 , we find Q(6) = (1 million) ek(6)
        = (1 million) ek(2)(3) = (1 million) [ek(2)]3
        = (1 million) [ 23] = 8 million
Thus Jake's body holds 8 million flu viruses at 6 PM