In today's notation of Roman numerals XIX represents 19
But during the Roman era the equivalent of 19 was XVIIII which was simplified to IXX and in fact its Latin word is undeviginti which means one from twenty.
DCLXVIII = 668
MCMLXXXV
DCCLXXIII
MM
XXXII = 32
19
XXXIII
It is: cmxx or CMXX = 920
It is M which means 1000
91 in Roman numerals is XCI (-10+101=91)
As Roman numerals they are: III, XXVIII and II respectively
XIX is 19 in Roman numerals.