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2/3-6*x = 8/21-5*x // - 8/21-5*x
2/3-6*x-(-5*x)-(8/21) = 0
5*x-6*x+2/3-8/21 = 0
2/7-x = 0 // - 2/7
-x = -2/7 // * -1
x = 2/7
x = 2/7
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