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(6/7)*x-(7*x)+5 = 19/21 // - 19/21
(6/7)*x-(7*x)-(19/21)+5 = 0
(6/7)*x-7*x-19/21+5 = 0
86/21-43/7*x = 0 // - 86/21
-43/7*x = -86/21 // : -43/7
x = -86/21/(-43/7)
x = 2/3
x = 2/3
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