Answer:
225 p/p
Step-by-step explanation:
This design consists of 3 groups of participants, each with 25 members and three case studies, thus:
case (1) 17 inch ----------- 25 members
case (2) 18 inch ----------- 25 members
case (3) 21 inch ----------- 25 members
Total: case = 3 ----------- 75 members
Total pieces of paper = 3*75 = 225 piece of paper