115-6*X=73 (4900/Y-280)/60=7
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(это проверка)
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115-6*х=73
6*х=115-73
6х=42
х=42:6
х=7
115-6*7=73
73=73
4900:у-280):60=7
(4900:у-280)=7*60
4900:у=420+280
4900:у=700
у=4900:700
у=7
(4900:7-280):60=7
7=7