Dan can do a job alone in 15 hours. Annie, working alone, can do the same job in just 10 hours. If Dan works alone for 6 hours and then stops, how many hours will it take Annie, working alone, to complete the job? Choose the correct choice from the following choices
A) 2 B) 4 C) 6 D) 8 E) 10
Dan can complete 1/15 of the job per hour.   In 6 hours, Dan completes 6(1/15) = 2/5 of the job.   Annie can complete 1/10 of the job per hour.   To complete the job, Annie will take 3/5 / 1/10 = 6 hours.   The answer is 6.
<result>C</result>
Dan can do a job alone in 15 hours. Annie, working alone, can do the same job in just 10 hours. If Dan works alone for 6 hours and then stops, how many hours will it take Annie, working alone, to complete the job?