Dan can do a job alone in 12 hours. Annie, working alone, can do the same job in just 9 hours. If Dan works alone for 8 hours and then stops, how many hours will it take Annie, working alone, to complete the job? Choose the most appropriate option
A) 2
B) 3
C) 4
D) 5
E) 6

Rationale: dan can complete 1 / 12 of the job per hour . in 8 hours , dan completes 8 ( 1 / 12 ) = 2 / 3 of the job . annie can complete 1 / 9 of the job per hour . to complete the job , annie will take 1 / 3 / 1 / 9 = 3 hours . the answer is b .
Answer: B