Hi bigdan, best not to put (urgent) in the title of your thread. It usaully has the opposite desired result if you know what I mean?!

We also preffered not to be annoyed.

Anyhow

using [tex]P = P_0e^{kt}[/tex] with the information given and assuming t represents months you need to solve for k given

[tex]3 = e^{10k}[/tex] what do you get?

After you have that value, solve for t when [tex]4 = e^{kt}[/tex]