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