[tex]2(a+b)=p\qquad\text{divide both sides by 2}\\\\a+b=\dfrac{p}{2}\qquad\text{subtract a from both sides}\\\\\boxed{b=\dfrac{p}{2}-a}\\\\or\\\\2(a+b)=p\qquad\text{use distributive property}\\\\2a+2b=p\qquad\text{subtract 2a from both sides}\\\\2b=p-2a\qquad\text{divide both sides by 2}\\\\\boxed{b=\dfrac{p-2a}{2}}[/tex]
