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b in (-oo:+oo)
-13/40 = b+3/8 // - b+3/8
-b-13/40-(3/8) = 0
-b-13/40-3/8 = 0
-b-7/10 = 0 // + 7/10
-b = 7/10 // * -1
b = -7/10
b = -7/10
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