Machine A can process 6000 envelopes in 3 hours. Machines B and C working together but independently can process the same number of envelopes in 2.5 hours. If Machines A and C working together but independently process 3000 envelopes in 1 hour, then how many hours would it take Machine B to process 12000 envelopes.	Pick.
A) 2 B) 3 C) 4 D) 6 E) 60/7
For 1 hour-   Machine A rate- 2000 envelopes   Machine B+C rate- 2400 envelopes   Since A + C = 3000 envelopes A's rate is 2000 envelopes as above, C has a rate of 1000 envelopes per hour.   Which makes machine B's rate as 1400 envelopes per hour.   Thus, it will take 8 hours to manufacture 12000 envelopes.   Answer:-60/7
<result>E</result>
Machine A can process 6000 envelopes in 3 hours. Machines B and C working together but independently can process the same number of envelopes in 2.5 hours. If Machines A and C working together but independently process 3000 envelopes in 1 hour, then how many hours would it take Machine B to process 12000 envelopes.