A consumer group conducted a study regarding the number of hours of TV that teenagers watched per week

A consumer group conducted a study regarding the number of hours of TV that teenagers watched per week. The cumulative frequencies of the sample were as follows.

Hours per week Cumulative Frequency
0-4 7
5-9 25
10-14 49
15-19 77
20-24 120

What is the mean "weekly hours of TV watched" for the sample?
a.) .38
b.) 12
c.) 15.42
d.) 17
e.) 370