Answer:
15 lessons for $ 80
Explanation:
In case 1
Cost of 1 lesson = $10
In case 2
Cost of 1 lesson = 40/5 = $8
In case 3
Cost of 1 lesson = 80/10 = $8
In case 4
Cost of 1 lesson = 80/15 = $ 5.33
Hence,
The best deal is case 4 i.e 15 lessons for $ 80