560:Х=80, Х=560:80, Х=7
42:Х=72-66, 42:Х=6, Х=42:6, Х=7
(х - 4 17/35) - 1 11/28 = 2 1/140
х - 4 17/35 = 2 1/140 + 1 11/28
х - 4 17/35 = 2 1/140 + 1 55/140
х - 4 17/35 = 3 56/140
х = 3 56/140 + 4 17/35
х = 3 56/140 + 4 68/140
х = 7 124/140
х = 7 31/35
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Проверка: (7 31/35 - 4 17/35) - 1 11/28 = 2 1/140
3 14/35 - 1 11/28 = 2 1/140
3 56/140 - 1 55/140 = 2 1/140
2 1/140 = 2 1/140
(6+5+10+12+15+20):6= 68/6= 34/3= 11 1/3