Answer:
[tex]\large\boxed{b=\dfrac{S}{3\pi r}-1}[/tex]
Step-by-step explanation:
[tex]3\pi rb+3\pi r=S\qquad\text{divide both sides by}\ 3\pi r\neq0\\\\\dfrac{3\pi rb}{3\pi r}+\dfrac{3\pi r}{3\pi r}=\dfrac{S}{3\pi r}\\\\b+1=\dfrac{S}{3\pi r}\qquad\text{subtract 1 from both sides}\\\\b=\dfrac{S}{3\pi r}-1[/tex]
