Schools grading scale

So I’m just trying to figure out a way to challenge my schools grading scale. They use a jupiter system and according the schools policy you have to have a cumulative grade of 78 on your exams before they add your out of class works, projects, and other assignments that you work so hard to get done in order to pass the class. Then if u don’t get the 78 for ur exams they’ll deduct the amount u would’ve got from your out of class assignments. Now is this fair to anyone? How could I fight this grading policy I’m not sure if this is legal or if this school have the right to grade like this?