I have 4/four classes today, but the fourth period is free so I'll have to stay on campus from 9 a.m. to 7 p.m. I think it's a little hard, but I'll do my best because today is the last day I have/need to go to university this week.

I have four classes today, but the fourth period is free, so I have to stay at the university from 9 AM to 7 PM. I think it's a little hard, but I'll do my best because today is the last day I have to go to university this week.