Don't use the pythagorean theorem on right triangles. Instead, you should memorize the most common special triangles, two of which are here. The triangle on the left can be recognized as a 30-60-90 triangle because the hypotenuse is double one of the legs. The ratio of the sides is 1-√3-2, which means x on this triangle should be 4√3.

The triangle on the right is a 45-45-90 triangle, recognizable because the two legs are the same length. The ratio of the sides is 1-1-√2, which means y on this triangle should be 4√2.

Since 4√3 is greater than 4√2, the answer is A.