15 7/39 - (11 4/39 - у) = 6 19/39
15 7/39 - 11 4/39 + у = 6 19/39
4 3/39 + у = 6 19/39
у = 6 19/39 - 4 3/39
у = 2 целых 16/39
Проверка: 15 7/39 - (11 4/39 - 2 16/39) = 6 19/39
15 7/39 - (10 43/39 - 2 16/39) = 6 19/39
14 46/39 - 8 27/39 = 6 19/39 - верно
