It would take one machine 4 hours to complete a large production order and another machine 3 hours to complete the same order. How many hours would it take both machines, working simultaneously at their respective constant rates, to complete the order?
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A\frac{7}{12}
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B{1}\frac{1}{2}
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C{1}\frac{5}{7}
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D{3}\frac{1}{2}
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E7