Answer:
x = 14
Step-by-step explanation:
The triangles are similar, so the ratios of corresponding sides are equal, that is
[tex]\frac{DF}{AC}[/tex] = [tex]\frac{EF}{BC}[/tex] , substitute values
[tex]\frac{x}{21}[/tex] = [tex]\frac{18}{27}[/tex] ( cross- multiply )
27x = 378 ( divide both sides by 27 )
x = 14
