Answer
D
Work Step by Step
Set up a ratio to find the missing length. Since the triangles are similar, the ratio between the lengths of corresponding sides is the same.
$\frac{5}{9}=\frac{7}{x}\longrightarrow$ cross multiply
$5x=63\longrightarrow$ divide each side by 5
$5x\div5=63\div5\longrightarrow$ divide
$x=12\frac{3}{5}$
