YOU SAID:
I walked the dog with this girl
INTO JAPANESE
私はこの女の子と犬の散歩をした
BACK INTO ENGLISH
I walked my dog with this girl.
INTO JAPANESE
私はこの女の子と一緒に犬の散歩をしました。
BACK INTO ENGLISH
I walked my dog with this girl.
You've done this before, haven't you.