Each x represents each student surveyed if count each x we will find that Janet surveyed
0 hours-- 1 student
1 hour -- 2 students
2 hours--3 students
3 hours -- 5 students
4 hours -- 1 student
5 hours -- 1 student
6 hours -- 3 students
7 hours -- 2 students
8 hours -- 2 students
If we sum them we will find that Janet surveyed 20 students