Easy Hold 'em Question

[FletchJr.]

Ok here's the situation,
I got KJs and I flop the flush.
There's another player in the pot and i figure he's got the Ace but he's not suited. What's the chances of him hitting the a 4th flush card on me.

I think it's like this
flop 3 cards seen, 2 in my hand. that's 5 flush cards seen. out of the 13, but then there's 1 i assume the opponent has. That means 6 cards out of 17 which leaves 7.
7/45(52-2(my hand)-2(his hand)-3(flop))
equals .1555555
river
7/44
equals .159090909
so I think I should add those two together.
done.
.31464646
But how do I find my chances I mean like 3.123 to 1,

So that's what i know, or think i know. But I'm sure it's easy to do, if someone could show me once. I shouldn't have a problem with any other math problems.(Hold'em anyways)
Thanks, Also I'd like to figure out exact percents, nothing close, exact figures rounded to like the 100th's.