Math Help - exponential word problem

1. exponential word problem

I need a little help as to how to start this one.

At noon, the population of a bacterial culture was 2.4 x 10^6. At 4pm., the population was 6.2 x 10^7. Assume exponential growth. When will the population be 8.2 x 10^8?

2. Try the model $P=P_0e^{kt}$

With P = population and t = hours

you can say for $(t,P) = (0,2.4 \times 10^6)$

therefore $P_0 = 2.4 \times 10^6$

$P=2.4 \times 10^6\times e^{kt}$

Now use $(t,P) = (4,6.2 \times 10^7)$ to solve for k and you will have your model

After this $8.2 \times 10^8$ goes into the model for P, solve for t.