## Algebra: A Combined Approach (4th Edition)

$20$ units
Step 1: Since the triangles are similar, their corresponding sides are in proportion. Step 2: This means that $\frac{9}{15}=\frac{12}{x}$. Step 3: Solving through cross multiplication: $9x=15\times12$. Step 4: $9x=180$ Step 5: $x=20$ units Check: Step 1: Equating the two proportions to see if they reduce to the same fraction: $\frac{9}{15}=\frac{12}{20}$ Step 2: Simplifying both sides: $\frac{3}{5}=\frac{3}{5}$ Step 3: Therefore, the answer is accurate.