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x in (-oo:+oo)
n+n-(5/6)+3/7 = (11/21)*x // - (11/21)*x
n+n-((11/21)*x)-(5/6)+3/7 = 0
n+n+(-11/21)*x-5/6+3/7 = 0
2*n-11/21*x-17/42 = 0 // - 2*n-17/42
-11/21*x = -(2*n-17/42) // : -11/21
x = (-(2*n-17/42))/(-11/21)
x = -21/11*(17/42-(2*n))
x = -21/11*(17/42-(2*n))
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