Symbols are written and read from left to right, from highest to lowest.'3475' look like in Roman numerals MMMCDLXXV.
MMMCDLXXV = 3475
M represents 1000, D is 500, C is 100 and L is 50. So this would be MMMCDLXXV.
If you mean in Roman numerals then in today's modern notation of Roman numerals it is now 3475 = MMMCDLXXV but the ancient Romans probably notated them quite differently.
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
MCMLXXXIX