A math question

I was looking at the tutor list and I think some people can give a hint or clue with this problem I have. I am in Calculus 2 and here is the problem.

A population grows at the rate of 1.5%. How long will it take the population to double?

I think I know what formula to use and it is one of the Differential Equations. It is Y=Ce^(kt). But I don't know What is C and k??

C is your initial value (starting population), and k is the rate, .015

edit: erm. but your asking about doubling..so, C you could set to 1, and you need to find the value for t that will make y=2

Thanks man, now I think about it, it is right. Thanks for the hint. And t should be 46.20 years.

Glad to help. logarithms are annoying...but once the concepts are understood, very simple.