Where I live, the EMT-B class is a combined course, meaning you don't take xxx class here, zzz class there, and then combine your credits into the course. Even if you've already taken, say, a CPR course, you're not exempt from having to take it again when you enter EMT-B class. Like Febrifuge said, it's usually about 150 hours of classroom time combined with approx. 24 hours of field ride time, depending on where you live. I took it 7 years ago, then went to EMT-Intermediate. We still spent a great deal of time going over things we learned in EMT-B class. And the same happened when I went through paramedic training.
So, I guess what I'm trying to say is that, usually, there's no real need to take any pre-reqs for the class because they'll teach it all to you during the program. 🙂
Anyway, good luck to you!!! 😀 👍