Rule 3: A smaller numeral written to the left of a larger numeral is always subtracted from the larger numeral.

find this answer I will make you V=5-1=4 , IX=10-1=9XL=50-10=40. ,. XC=100-10=90

find this answer I will make you V=5-1=4 , IX=10-1=9XL=50-10=40. ,. XC=100-10=90