Hi all!

My math problem is about a Finance class, but it is really the math that gets me into trouble. Please see the equation:

$\displaystyle \dfrac{15}{(1+r)}+\dfrac{10}{(1+r)^2}+\dfrac{8}{(1 +r)^3}-25=\dfrac{2.5}{(1+r)}+ \dfrac{2.5}{(1+r)^2}+\dfrac{2.5}{(1+r)^3}$

I guess the first step would be to get it all to one side of the equation. In particular, I am wondering what to do with the denominators. Can I add them up?

Please note I'm only allowed to use a basic (i.e. non-graphic) calculator.

Thank you!

Sebastiaan