The original problem has to do with the interest rate at which 2 choices have the same present value, but I figured out the equation on my own. For some reason, I can't figure out how to solve it, even though I'm usually very comfortable with solving algebraic equations...

6000 + (5940)/(1+i) =12000/[(1+i)^(1/2)]

The answer is i = .21 (answer in the back of the book, works when plugged in) but I can't figure out how to get it.