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x in (-oo:+oo)
2/7-x = -13/28 // + -13/28
2/7-x-(-13/28) = 0
2/7-x+13/28 = 0
3/4-x = 0 // - 3/4
-x = -3/4 // * -1
x = 3/4
x = 3/4
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