Because of changes to the rules governing the Roman numeral system today we would convert 19 into Roman numerals as XIX.
But during the Roman era the equivalent of 19 was XVIIII and it was probably simplified to IXX (-1+20=19) because the Latin word for IXX literally means one from twenty.
roman numarals are v,i ,x,c and some other stuff with represent numbers
XII
L
Your answer is XXI
CCCLXII
DCC
1 = I
XXXIX
538
XII
CXXVI
in roman X