The 600 would be represented by 500 (D) plus 100 ( c ). And 40 is made by subtracting 10 (X) from 50 (L). So 645 would be DCXLV.
Dcxlv dcxlv=500+100+(50-10)+5=600+40+5=645
In today's notation 645 = DCXLV in Roman numerals
645 = DCXLV
the answer to what is the roman numeral for 101 is CI
'XXV' is the Roman Numeral. I think you wish to know the Arabic (Modern) number, which is '25'.
No, K is not a roman numeral.
There is not a Roman Numeral for 0.
The roman numeral for one is I.
Vivid is not a Roman numeral
M is a roman numeral that represents 1000.
V is a roman numeral representing the number 5.
The number 80 is represented by the Roman numeral LXXX