Answer
9
Work Step by Step
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
$\frac{18}{2}=$
$9$
