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b in (-oo:+oo)
2/7-((2/3)*b) = 76/21 // - 76/21
2/7-((2/3)*b)-(76/21) = 0
(-2/3)*b+2/7-76/21 = 0
-2/3*b-10/3 = 0 // + 10/3
-2/3*b = 10/3 // : -2/3
b = 10/3/(-2/3)
b = -5
b = -5
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