(х - 42) + 17 = 62
х - 42 = 62 - 17
х - 42 = 45
х = 45 + 42
х = 87
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Проверка: (87 - 42) + 17 = 62
45 + 17 = 62
62 = 62
(х * 12) : 4 = 18
х * 12 = 18 * 4
х * 12 = 72
х = 72 : 12
х = 6
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Проверка: (6 * 12) : 4 = 18
72 : 4 = 18
18 = 18