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k in (-oo:+oo)
5*k+1/3 = (-3/4)*k+221/42 // - (-3/4)*k+221/42
5*k-((-3/4)*k)+1/3-(221/42) = 0
5*k+(3/4)*k+1/3-221/42 = 0
23/4*k-69/14 = 0 // + 69/14
23/4*k = 69/14 // : 23/4
k = 69/14/23/4
k = 6/7
k = 6/7
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