What is the length of the missing side of the larger triangle?

Answer:
B
Step-by-step explanation:
Since the triangles are similar then the ratios of corresponding sides are equal, that is
[tex]\frac{?}{6}[/tex] = [tex]\frac{18}{12}[/tex] ( cross- multiply )
12 ? = 108 ( divide both sides by 12 )
? = 9 → B