Each mapping represents the number of letters in the spelling of the word:
1 one - 3 letters
2 two - 3 letters
3 three - 5 letters
...
11 eleven - 6 letters
12 twelve - 6 letters
The ? Represents 6.
1 one - 3 letters
2 two - 3 letters
3 three - 5 letters
...
11 eleven - 6 letters
12 twelve - 6 letters
The ? Represents 6.