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k in (-oo:+oo)
(2/5)*(5*k+3*k)-8 = 12 // - 12
(2/5)*(5*k+3*k)-12-8 = 0
2/5*8*k-12-8 = 0
2/5*8*k-12-8 = 0
16/5*k-12-8 = 0
16/5*k-20 = 0
16/5*k-20 = 0
16/5*k-20 = 0 // + 20
16/5*k = 20 // : 16/5
k = 20/16/5
k = 25/4
k = 25/4
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