Crossword Genius

There’s a number on her back (4)

Ross

I believe the answer is:

nola

I'm a little stuck... Click here to teach me more about this clue!

'back' is the definition.
I don't know anything about this answer so I cannot judge whether this works.

'there's a number on her' is the wordplay.
'there's a number' becomes 'n' (n can represent any number).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'her' becomes 'ola' ().
'n'+'ola'='NOLA'

Can you help me to learn more?

I've seen this clue in the Evening Standard.
Want a hint initially instead of a full solution? Install my app