What is the ruling on taking one subject from expensive private lessons and sharing its cost among students to reduce the expense?

It is permissible for a female student to explain what she has understood from a lesson to her peers. However, giving them the teacher's notes depends on his permission. If the teacher forbids it, then it is not permissible to copy or photograph the notes except with his permission, in order to preserve his right. Some scholars, however, permit this for personal need and benefit, but not for commercial purposes.