Answer: 200/7
Explanation:
This creates 3 similar right triangle
you would put similar parts on top and the similar parts on bottom of proportions.
ex.

in your problem they gave the short legs and long legs of right triangel
The line that they share in middle of the triangle is the long leg for the triangle on right and it is also the short leg for triangle on left.


x=(400)/14 = 200/7
You could also make your proportion where
parts of 1 triangle = equivalent parts of the other
ex.
