Hmmmmm.....it's been awhile, but I think it's X.
More than that, it's infinite!
I had the same problem. Never could see how to add, multiply or divide freakin' letters! Failed it with gusto every time. That being said, I do realize, after all these years, that I use it in ways I never would guess and do OK with it as long as I don't think of it as "algebra".