11 = xi 12 = xii 13 = xiii
14 = xiv 15 = xv 16 = xvi
17 = xvii 18 = xviii
19 = xix 20 = xx
12 = XII in Roman numerals
18 in roman numerals looks like XVIII
The Roman numerals are XLV.
300 would be represented by 'CCC' in roman numerals.
MDCCCXCV
MMDCCCLXXXVI
MCMLXXXV
MCMLXV
MCMLII
XXI
DCLXVI
MCMLXXXIX