It takes the first pipe 9 more hours to fill the pool than the first and the second

QuestionsCategory: MathIt takes the first pipe 9 more hours to fill the pool than the first and the second
Lisa Howell asked 5 months ago
It takes the first pipe 9 more hours to fill the pool than the first and the second pipes together and 7 less hours than it would take the second pipe if it was working alone. How long would it take to fill up the pool if both pipes were working together?

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