conversations.from: human
conversations.value: It takes 10 minutes to wash a car, 15 minutes to change oil, and 30 minutes to change a set of tires.  If mike washes 9 cars, changes the oil on 6 cars, and changes two sets of tires how many hours did he work?
conversations.from: assistant
conversations.value: He spent 10 minutes *9 cars = 90 minutes washing cars
  He spent another 15 minutes * 6 cars = 90 minutes changing oil.
  He spent 2 cars * 30 minutes = 60 minutes changing tires.
  He spent 90 minutes + 90 minutes + 60 minutes = 240 minutes working
  He spent 240 minutes / 60 minutes = 4 hours working