I have a doubt in roman numericals

Question

The below question, I am looking at the 80, They translated it as LXXX, but I can also write it as XXC right?

Answer 1

Generally, in Roman numerals, you can't subtract more than one thing. For example, IV is $4$, but $3$ can't be written IIV. So XC would be 90, but XXC is meaningless.

Answer 2

Reese is right.

Plus: you cannot do IC or IL or VC or XM, etc. Only certain very specific cases are allowed for subtraction.

These restrictions are how we do it nowadays. But the classical Romans themselves may not have been so strict. I posted HERE a copy of a pre-Julian Roman calendar, where the number of days in February is written as XXIIX ...