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x in (-oo:+oo)
26/6 = x/21 // - x/21
26/6-(x/21) = 0
13/3-1/21*x = 0 // - 13/3
-1/21*x = -13/3 // : -1/21
x = -13/3/(-1/21)
x = 91
x = 91
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