Math Puzzle... For The Rest of Us!

I don't know about you guys, but my head is still spinning from UEA and Cardiac Linfarction's recent Mathspin posts. Standardized test scores to the contrary notwithstanding, I'm sure I'm not as smart as those guys, but recently I was able to solve a pretty tough math question, so I figured I'd post it here as a pre-Labor Day puzzle for us regular folks.

Reply to any of my comments with your best guess — I'll see it in my inbox. And good luck!