Because he has 20 lessons a week, and is late 7 times a lesson, we know that he misses 20*7 minutes a week.
Because there are 38 weeks a year, we multiply the unit rate by 38:
38*140 = 5320
Because we're looking for hours, not minutes, we divide by 60:
5320/60
532/6
8 (4/6)
8 2/3 hours
