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

If any two triangles are similar, then their corresponding sides are in proportion. Thus, the proportion of the given sides: $\frac{8}{x}$ = $\frac{10}{15}$ Cross multiplying both sides, we get 15(8) = 10(x). Thus 120 = 10x. Dividing both sides by 10, we get $\frac{10x}{10}$ = $\frac{120}{10}$. Thus, x = 12.