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

Evaluate $\frac{x+y}{2}$ when y is twice x and x is 6. Write an expression for y in terms of x. $y=2x\longrightarrow$ Substitute for x to find y. $y=2(6)=12$ $\frac{x+y}{2}=\longrightarrow$ Substitute for x and y in the original formula. $\frac{6+12}{2}=\longrightarrow$ Solve $\frac{18}{2}=$ $9$