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k in (-oo:+oo)
7*(5*k-8) = 259 // - 259
7*(5*k-8)-259 = 0
7*(5*k-8)-259 = 0
35*k-315 = 0
35*k-315 = 0
35*k-315 = 0 // + 315
35*k = 315 // : 35
k = 315/35
k = 9
k = 9
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