Answer :
12 because when you make the equation:
[tex]C= \frac{B+6}{2} [/tex]
Then you plug it in with 9 for C:
[tex]18= \frac{B+6}{2} [/tex]
Solve for B and you get:
B=12
[tex]C= \frac{B+6}{2} [/tex]
Then you plug it in with 9 for C:
[tex]18= \frac{B+6}{2} [/tex]
Solve for B and you get:
B=12