we have
[tex] y=3x+3b [/tex]
solve for b (clear variable b)
Adds -3x on both sides
[tex] y-3x=3x+3b-3x\\ 3b=y-3x [/tex]
Divide by 3 on both sides
[tex] \frac{3b}{3} =\frac{y}{3} -\frac{3x}{3} \\ \\ b=\frac{y}{3}-x [/tex]
therefore
the answer is
[tex] b=\frac{y}{3}-x [/tex]
