"Are you answering him?"
Translation:אתן עונות לו?
The verb "to answer", לענות, is always followed by ל, because effectively you are answering to someone.
You could say "אתה עונה לו" When it says you, it could be את, אתה, אתם and אתן English does not differ in plurality or gender, and it has to be figured out by context what "you" means. In Hebrew it is not that ambiguous.