I'm guessing that you know about 45-45-90 and 30-60-90 triangles.
In 45-45-90 triangles, the legs are in a ratio such that the hypotenuse is times the legs.
In 30-60-90 triangles, the legs are in a ratio of 1::2
In the picture given we have been given a value of the side of the 45-45-90 triangle. We can deduce that the value of the hypotenuse is 9 because of the ratio of the sides of a 45-45-90 triangle.
The 30-60-90 triangle shares the same hypotenuse, and so we now know a value of one of its sides as well. The ratio of the side of value 'x' and the hypotenuse is : 2
We can create an equation to solve for x using these ratios:
=
Cross multiply:
2x = 9
x =
Option C