A and B can complete a job in 36 and 36 days. They start together but A leaves after working for 24 days. How long would B take to finish the job counting from the day both A and B started together?
If B takes x days. The total job is A's work in 4 days + B's work in x days = $24/36$ + $x/36$ = 1. Solving, we get x = 12 days.