Jones can paint a car in 8 hours. Smith can paint the same car in 6 hours. They start to paint the car together. After 2 hours; jones leaves for lunch and smith finishes the car alone. How long does it take smith to finish?
in two hours, they have done
2(1/8 + 1/6) = 7/12 of the job
since Smith does 1/6 of the job per hour, it will take him
7/12 ÷ 1/6 = ____ more hours