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123/35 = (-1/5)*x+(5/7)*x+3 // - (-1/5)*x+(5/7)*x+3
123/35-((-1/5)*x)-((5/7)*x)-3 = 0
(1/5)*x+(-5/7)*x+123/35-3 = 0
18/35-18/35*x = 0 // - 18/35
-18/35*x = -18/35 // : -18/35
x = -18/35/(-18/35)
x = 1
x = 1
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