How do I correct this (details inside)

Disclaimer: despite a reference to an assignment here, this is definitely not a homework question. This is an English usage question.

OK, here’s the background story: a few days ago our teacher gave us a writing assignment as a homework. The topic was something like: “Write a letter to your English friend to apologize for having to delay his/her visit to your home next month and explain the reason”. This morning we handed our papers down to the teacher. She then asked us to exchanged our papers, making sure each student had the paper of someone other than himself/herself, and correct all the grammatical mistakes before giving it back to her.
I got the papers of a boy who wrote something like this: ”...I’ll see you at 10th next month”. At 10th next month? I have a feeling he was literally translating every word of his language into English. But I’m not sure if he was right or not, let alone what the equivalent phrase to that in English is. The boy was sure he was right, and I didn’t (couldn’t) correct it.
Can you point out what the correct phrase is?