Use the Accompanying Diagram, Which Contains Two Similar Triangles

Multiple Choice

$\begin{array}{|l|c|c|}\hline {\text { Item }} & \text { Quantity Needed } & \text { Cost } \\\hline 8 \text { Spark plugs } & 1 \text { set } & \$ 31.84 \\\text { Spark plug wires } & 1 \text { set } & \$ 73.92 \\\text { Distributor cap } & 1 & \$ 24.16 \\\text { Rotor } & 1 & \$ 9.10 \text { each } \\\text { Labor } & \text { Flat rate } & \$ 80.00 \\5 \% \text { sales tax on } & & \\\text { parts only } & & \\\hline\end{array}$ Use the accompanying diagram, which contains two similar triangles. If side a is 2 inches, side b is 9 inches, and side B is 18 inches, find side A in inches.

A) 3
B) 4
C) 5
D) 6