To rewrite the equation \(9b + 12\) by dividing by 3, you can factor out 3 from both terms:
\[ 9b + 12 = 3(3b + 4) \]
So, if you divide the whole expression by 3, you get:
\[ \frac{9b + 12}{3} = 3b + 4 \]
Thus, the equation simplifies to:
\[ 3b + 4 \]