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(-1/7 + x) - 1/14 = 2 1/3
x - 3/14 = 2 1/3
x = 2 1/3 + 3/14
x = 98/42 + 9/42
x = 107/42
x = 2 23/42

(-1/7 + 2 23/42) - 1/14 = 2 2/3
2 17/42 - 3/42 = 2 2/3
2 14/42 = 2 2/3
2 2/3 = 2 2/3

Ответ: {2 23/42}