It takes Doug 6 days to reroof a house. If Doug's son helps him, the job can be completed in 4 days. How long would it take Doug's son, working alone, to do the job?
rate of doug is 1 roof in 6 days. which means he could do 2/3 of a roof in 4 days, whixh means his son does 1/3 of a roof in 4 days, whhich is 1 roof per 12 days.