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b in (-oo:+oo)
40 = 5*b-b+4 // - 5*b-b+4
b-(5*b)-4+40 = 0
b-5*b-4+40 = 0
36-4*b = 0 // - 36
-4*b = -36 // : -4
b = -36/(-4)
b = 9
b = 9
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