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

Rationale: "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 c ."
Answer: C