When Mina’s 같이공부해요 is a suggestion to act together, report 미나가같이공부하자고했어요. Do not turn it into a statement that she studies alone or an instruction to study.
Original expression
Reported expression
같이가요. (제안)
같이가자고했어요.
같이먹어요. (제안)
같이먹자고했어요.
같이공부해요. (제안)
같이공부하자고했어요.
자료를함께만들어요. (제안)
자료를함께만들자고했어요.
Attach -자고 to the verb stem: 가자고, 먹자고, 만들자고. Do not insert 으 because of a final consonant. Use context to establish that 같이가요 is a suggestion.