Several identical inlets and outlets open together

This type of question, asked 3 times: 14 Jul 2023 S3, 20 Jul 2023 S1, 26 Jul 2023 S2. All 3 questions below, oldest first.

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Question 1
14 Jul 2023 S3
74 $An inlet pipe can fill an empty tank in 140 hours while an outlet pipe drains a completely-filled tank in 63 hours. If 8 inlet pipes and y outlet pipes are opened simultaneously, when the tank is empty, then the tank gets completely filled in 105 hours. Find the value of y.$
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Question 2
20 Jul 2023 S1
53 $An inlet pipe can fill an empty tank in 120 hours while an outlet pipe drains a completely-filled tank in 54 hours. If 8 inlet pipes and 3 outlet pipes are opened simultaneously, when the tank is empty, then in how many hours will the tank get completely filled?$
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Question 3
26 Jul 2023 S2
67 $Each inlet pipe can fill an empty cistern in 84 hours while each drain pipe can empty the same cistern from a filled condition in 105 hours. When the cistern is empty, 9 inlet pipes and 10 outlet pipes are simultaneously opened. After how many hours will the cistern be completely filled?$
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Question 1