What is the ruling on combining the Maghrib and Isha prayers at the time of Isha due to studying at the institute and being unable to pray inside the institute?

Studying is not a valid excuse for combining prayers; they must be performed at their appointed times. If the time for prayer arrives while you are in class, ask permission, perform the prayer, and then return. Whoever delays a prayer, whether with or without an excuse, until the time of the next prayer has begun, is obligated to make it up and repent in the case of delay without excuse. The missed prayer should be made up first, even if that leads to the current prayer's time expiring.