John can paint a fence in 15 hours. his brother can paint it in 18 hours. If john paints for 8 hours alone and turns the rest over to his brother, how long will it take his brother to finish painting the fence?

after 8 hours john has done 8/15 of the job. We can set up a proportion to determine how long his brother will take:

that is 8 hours and 24 minutes