(12 5/13 + у) - 9 9/13 = 7 7/13
12 5/13 + у = 7 7/13 + 9 9/13
12 5/13 + у = 16 16/13
у = 16 16/13 - 12 5/13
у = 4 11/13
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Проверка: (12 5/13 + 4 11/13) - 9 9/13 = 7 7/13
16 16/13 - 9 9/13 = 7 7/13
7 7/13 = 7 7/13
0,77:(-0,2)= -3.85 ответ -3.85