Romans used another system of numbers, very difficult to do any math calculations with, and missing the concept of zero. The Arabic numerals we use today successfully replaced the unwieldy Roman numerals.
roman numarals are v,i ,x,c and some other stuff with represent numbers
XII
Your answer is XXI
L
CCCLXII
XII
538
1 = I
DCC
XXXIX
in roman X
CXXVI