A type T machine can complete a job in 5 hours and a type B machine can complete the job in 7 hours. How many hours will it take 2 type T machines and 3 type B machines working together and independently to complete the job?  Pick one:
A) 1 / 5
B) 29 / 35
C) 5 / 6
D) 35 / 29
E) 35 / 12

Rationale: now d should be the answer . t need 5 hours to complete and b needs 7 hours to compete so 2 t + 3 b will complete 2 / 5 + 3 / 7 or 29 / 35 portion of the job in 1 hour so the whole job will take 35 / 29 hours . . . . = d
Answer: D