It's easy to assume that online quizzes are meant for the average intellect, but while most of them aren't exactly an IQ test or even the Stanford Achievement Tests we all used to take when we were in school, it doesn't mean that they're always easy. Some of the puzzles can be really darn challenging and make you think. Of course it's not going to make you burn the few useful brain cells you have in your head but it might make you sweat a bit as you try to solve them.
Of course it wouldn't be a puzzle if you could actually solve it in two seconds. What would be the fun in that?
And here's a hint, it's not 6. So don't even go there. Okay?
Come on! Start by closing your mouth before you let some flies in and put on your thinking cap.
If you learn to think differently than the way you usually would then you might just have a chance to beat the challenge.
See? Told you it was all about thinking beyond the scope of what you were seeing. But don't feel too bad. You're not the first person to get it wrong.