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(5/7)*x-(3/10) = 23/90 // - 23/90
(5/7)*x-(3/10)-(23/90) = 0
(5/7)*x-3/10-23/90 = 0
5/7*x-5/9 = 0 // + 5/9
5/7*x = 5/9 // : 5/7
x = 5/9/5/7
x = 7/9
x = 7/9
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