## Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

$$r=\frac{b}{a+c};\quad \:a\ne \:-c$$
Solving the equation by using the rules of Algebra to isolate the given variable, we obtain: $$ar+cr=b\\ r\left(a+c\right)=b\\ r=\frac{b}{a+c};\quad \:a\ne \:-c$$