30 students volunteered to set up booths for the school fair. All of the students worked 2 hours after school on Thursday and on Friday. This means the total number of hour worked on Thursday is 30 × 2 = 60 hours and Friday is 30 × 2 = 60 hours
Twelve of them also worked 3 hours on Wednesday. It means that the total number of hour worked on Wednesday is
12 × 3 = 36 hours
If they did this for 2 weeks, it means that they worked for 2 Wednesdays, 2 Thursdays and 2 Fridays.