DCC = 500+100+100 = 700
21+22 = 43 = XLIII
they wrote on wax
Romans wrote on paper made from reeds. They also wrote on animal skins, but the animal skins and paper were to expensive for school kids to write on so they wrote on wax tablets. When they were done...
Well, in my free time I invented this thing called the calculator. I'll mail you one.