Quick Algebra question (logs and stuff)

I'm having trouble with this word problem:

Assume $150 is deposited in a savings account. If the interest rate is 4.5% compounded continuously, after how many years will the investment be worth $450? (Round your answer to the nearest month.)

I start off with

$\displaystyle y=ae^{rt}$

$\displaystyle 450=150e^{4.5t}$

$\displaystyle 3=e^{4.5t}$

$\displaystyle \ln(3)=4.5t\ln(e)$

after this, my teacher says i did something wrong, but i can't figure out where i did it wrong.