Area of segments - circle help

I need some help with a puzzle that has been really bugging me. I can't think of any solutions without getting more information, and I have no idea how to get that information.

*You have two identical circles that overlap (like a venn diagram) so that the center point of one circle is on the edge of the other circle. If the overlapping area is exactly 20000 square centimetres, what is the radius of the circles?*

Either answers or suggestions on how to reach an answer would be great. I know the information is vague... Hence the fact I can't do it ^^