It is: (IV) which means 1000*[5-1] = 4000
The number 4000 in Roman numerals is represented as "MMMM".
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
XXI
DCLXVI
MCMLII
MCMLXXXIX