Answer: Second option.
Explanation:
By the Right Triangle Altitude Theorem, we know that the altitude "h" (Observe the figure attached) is:

Then, since we know the value of the altitude, we can calculate the value of "y" with the Pythagorean Theorem:

Where "a" is the hypotenuse and "b" and "c" are the legs of the right triangle.
We can identify that:

Then, substituting values, you get that "y" is:
