(х - 1) * 9 = (5 - х) * 2
х * 9 - 1 * 9 = 5 * 2 - х * 2
9х - 9 = 10 - 2х
9х + 2х = 10 + 9
11х = 19
х = 19/11
х = 1 целая 8/11
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Проверка:
(1 8/11 - 1) * 9 = (5 - 1 8/11) * 2
8/11 * 9 = 3 3/11 * 2
72/11 = 36/11 * 2
72/11 = 72/11