It takes Master Wang 4 hours and master Li 6 hours to process a batch of machine parts? Don't use XY, list the formula

Alas, this kind of practical problem has been done in primary school~
Assuming that this batch of machine parts is in one unit, Master Wang can do 1 / 4 in one hour, and master Li can do 1 / 6 in one hour. If they work together for one hour, that is (1 / 4 + 1 / 6 = 5 / 12). If they divide the unit by 5 / 12, they get 12 / 5. Therefore, Master Wang and master Li work together for 12 / 5 hours, that is, 2.4 hours, 24 minutes or 144 minutes

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