Answer:
Step-by-step explanation:
Since the whole right side of that triangle is equal to 28 and the lower portion is 21, then we know the upper portion is 7. Set up a proportion using those sides and the fact that the 2 triangles are similar:
[tex]\frac{7}{21} =\frac{x}{18}[/tex] and cross multiply to get
21x = 126 and
x = 6
