xviii
18 written in Roman numerals is XVIII.
The date 18-06-1990 in Roman numerals would be XVIII.VI.MCMXC
XVIII
In todays notation of Roman numerals: V-XVIII-MCMXCII
XVIII-XI-MMX
XI-XVIII-MMX
It is: II-XVIII-MMXI
Xviii/xi/mxvim
It is: X-XVIII-MMX
18 - XVIII
A similar question to this has been recently answered in the Roman Numerals category.
The roman numerals for April 18, 1989 are XVIII.IV.MCMLXXXIX.