KöMaL 2020 C1602

Two tenth-grade students and two eleventh-grade students sat down to solve the exercises of type C in the April issue of KöMaL. (There are seven exercises each month. Exercises 1-5 are for students in grade 10 at most, while exercises 3-7 may be solved by 11th and 12th grade students.) After an hour, they observed that each exercise was solved by exactly one of them, and that everyone solved at least one exercise. In how many different arrangements may they have solved the exercises? (Two arrangements are considered different if there is at least one exercise that is solved by a different student.)