Answer:
-9
Step-by-step explanation:
9=b-2b
9=-b
divide both sides by -
b=-9
[tex] \boxed{b = 9} [/tex]
[tex] = > 2b + 9 = b \\ \\ = > 2b - b + 9 = 0 \\ \\ = > b + 9 = 0 \\ \\ = > b = - 9[/tex]
