Comment on Kid gave a reasonable answer without all the math bullshit
TaTTe@lemmy.world 2 days agoThe general rule is that the larger symbols come first in Roman numerals, so 12+10 (22) would be written as 10+10+1+1 or XXII.
If you literally meant the arithmetic 12+10, I’d assume they used some symbol for addition, so it would be written as XII+X, but I can’t say for sure.