I need some examples of how to wok out algebraic equations. For example: Suppose you deposit $2,374.00 into an account today. In 15.00 years the account is worth $3,988.00. The account earned ____% per year.

I've done the following:

3,988 = 2374 (1+r)^15

1.67 = (1+r)^15

And that is where I get stuck. The answer is 3.52%. How did they come up with that answer? I also have other questions that if I could see an example I could work them out myself.