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

Evaluate $\frac{a-b}{3}$ when a is 3 times b and a=18. Given the value of a, find b. $a=3b\longrightarrow$ Substitute for a. $18=3b\longrightarrow$ Divide both sides by 3. $18\div3=3b\div3\longrightarrow$ Solve. $6=b$ Substitute for a and b in the original equation. $\frac{a-b}{3}=\frac{18-6}{3}=\frac{12}{3}=4$