How many dozen pens is the man ordering?

Man: I need twelve dozen ballpoint pens.
Woman: Do you want any specific color?
Man: Oh, I hadn’t thought about that. Well, all right, I’ll take six dozen red pens, four dozen black, and two dozen purple.
Woman: I’ll have to check for the purple  Hmmm, according to our inventory list we have some in the back. I’ll have someone bring them out. Your total for 12 dozen pens comes to seventy-five dollars exactly, including tax.
Man: Let me see what I have in my wallet. Oh, yes, here’s a one-hundred dollar bill.