In todays terms: MCMXC
But the Romans probably wrote it out simply as XMM (2000-10)
1990 = MCMXC
XMM
The date 18-06-1990 in Roman numerals would be XVIII.VI.MCMXC
Roman numerals are a system for writing numbers, not words. the Roman numeral for 4 is IV.
XCVIII is 98 in Roman numerals
Roman numerals for 201 = CCI
1008 in Roman numberals is MVIII
DXXVII is the answer.
MMX
II
LXXV
MCCXXVIII