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k in (-oo:+oo)
(4/5)*k-7 = (3/5)*k+8 // - (3/5)*k+8
(4/5)*k-((3/5)*k)-8-7 = 0
(4/5)*k+(-3/5)*k-8-7 = 0
1/5*k-15 = 0 // + 15
1/5*k = 15 // : 1/5
k = 15/1/5
k = 75
k = 75
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