Answer:
3.4 lessons per week
Explanation:
If the teacher has to teach 6 chapter in 15 weeks, and each chapter has around 8.5 lessons. it means that the teacher has to teach in 15 weeks a total amount of lessons of 6*8.5= 51.
so 15 weeks---51 lessons
1 week------x
From the above relation we have= 51/15= 3,4 lessons per week