Working alone it takes Cody 6 hours to harvest a field. Kathryn can harvest the same field in 9 hours. How long would it take them if they worked together?

Heh, this is a tricky one. This would get you messed up, thinking it'd be 15 hours. But if they worked together, they would go faster, making it simple subtraction, which means 9-6 = 3.

3 hours. Have a great day.