If printing press A, running alone at its constant rate, produces 27,0

Given: Printing press A, running alone at its constant rate, produces 27,000 newspapers in six hours => 27000 newspapers in 6 hours.
27000/6 = 4500 newspaper in an hour.

To find: how long does it take printing press B, running alone at its constant rate, to produce 27,000 newspapers?

(1) Running alone at their respective constant rates, printing press B produces two newspapers in the same amount of time that printing press A produces three newspapers.

B prints 2/3 of newspaper what A print in a given time.
A print 4500 newspaper in 1 hour
4500/60 = 75 newspaper per second.

So B prints 50 newspapers per second.
27000 newspapers in 27000/50 = 540 minutes.
540 seconds = 9 hours
(Sufficient)

(2) Running together at their respective constant rates, the two presses produce 7,500 newspapers in one hour.
A prints 4500 newspapers in an hour
So, B prints 7500-4500 = 3000 newspapers
B will print 27000 newspapers in 27000/3000 = 9 hours
(Sufficient)

Answer is D

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