What about that third flop card ???

[BasketballNYC]

This may be a ridiculously simple probability question but I am not very good at calculating these things yet. I have seen the result for the probability of flopping a flush draw in hold'em when I have suited cards is 11%. Yet I do not know how that number was computed. If the flop were only two cards it would be easy. But what about that third opportunity. It has to make the number much bigger, but how is that calculated? Thanks for any help.

Matt F.