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(5/7)*x+(3/7)*x+2/3 = 254/21 // - 254/21
(5/7)*x+(3/7)*x+2/3-(254/21) = 0
(5/7)*x+(3/7)*x+2/3-254/21 = 0
8/7*x-80/7 = 0 // + 80/7
8/7*x = 80/7 // : 8/7
x = 80/7/8/7
x = 10
x = 10
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