Hey, I have run aground on what im sure is a fairly simple logarithmic problem. Any help would be appreciated.

How would I go about solving a combination exponential and logarithmic problem such as this one:

Population of a city is observed as growing according to function P(t) = p0e^kt where the population has doubled after the first 30 years

- Find k

- By what factor will original population have grown after 120 years...

I thought to find k it was an application of ln. But im not sure what numbers i should be substituting into the exponential formula and where.

Please help!

Thanks