Machine A can finish a job in 6 hours, Machine В can finish the job in 12 hours, and Machine С can finish the job in 8 hours. How many hours will it take for A, B, and С together to finish the job?	Choose the correct choice from the following answers:
A) 6 / 5 B) 7 / 4 C) 8 / 3 D) 9 / 2 E) 12 / 5

Rationale: the combined rate is 1 / 6 + 1 / 12 + 1 / 8 = 9 / 24 of the job per hour . the time to complete the job is 24 / 9 = 8 / 3 hours . the answer is c .
Answer: C