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k in (-oo:+oo)
4*k-7/10 = 257/90 // - 257/90
4*k-7/10-(257/90) = 0
4*k-7/10-257/90 = 0
4*k-32/9 = 0 // + 32/9
4*k = 32/9 // : 4
k = 32/9/4
k = 8/9
k = 8/9
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