There are no formal requirements about solving the exercise problems.
If you want a small bonus for the exam,
you can return your answers in written form (on paper or by email).
This is the only way to get a bonus.
You have to return your answers one day before the exercise session
(that is, on Monday).
Doing 75% of the exercises gives the maximum bonus.
The exercise sessions are meant for
discussing and going through the exercise problems.
Attendance is recommended but not required.