This is the 5230th most frequent Arabic word.
بهما
"بهما" means "with them" (dual form).
Here, 'بـ' + 'هما' denotes the pronoun 'both of them', referring back to the previously mentioned dual subject, the books.
لقد قرأت الكتابين وأعجبت بهما.
I have read the two books and am impressed with both of them.
The pronoun 'بـ' + 'هما' refers to 'both of them' as an object of the verb, combining 'بـ' (with) and 'هما' (both of them).
يجب أن تتحدث بهما مع الأستاذ.
You should speak with both of them to the teacher.
'بـهما' is used here as an instrumental pronoun referring to 'them' (dual form), showing association with the action.