Verified Answer :

3x-y/3=b, you are isolating b to the other side

we have

\(y=3x+3b\)

solve for b (clear variable b)

Adds -3x on both sides

\(y-3x=3x+3b-3x\\ 3b=y-3x\)

Divide by 3 on both sides

\(\frac{3b}{3} =\frac{y}{3} -\frac{3x}{3} \\ \\ b=\frac{y}{3}-x\)

therefore

the answer is

\(b=\frac{y}{3}-x\)