Working alone, Printers X, Y, and Z can do a certain printing job, consisting of a large number of pages, in 12, 15, and 18 hours, respectively. What is the ratio of the time it takes Printer X to do the job, working alone at its rate, to the time it takes Printers Y and Z to do the job, working together at their individual rates?



~$4 \over 11$~

~$1 \over 2$~

~$15 \over 22$~

~$22 \over 15$~

~$11 \over 4$~

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