Answer: Second option.
Step-by-step explanation:
As you can observe in the picture given in the exercise, there are two Right triangles formed inside the rectangle: CDA and ABC.
You need to use the Pythagorean Theorem to solve this exercise. This is:
Where "a" is the hypotenuse and "b" and "c" are the legs of the Right triangle.
If you solve for one of the legs, you get the following equation:
In this case, you can identify in the figure that:
Finally, you must substitute these known values into the equation and then evaluate in order to find the value of "x". You get that this is: