Let's say the side length of square A is x, which means the side length of square B is 2x.
Then, the area of square A can be written as , and the area of square B can be written as .
There's no diagram here with shaded region, so I'll just find the area of square A as a percentage of the area of square B:
= 1/4 = 25%
So, the answer is 25% (note this is the answer to the question: "express the area of square A as a percentage of the area of square B; there is no diagram showing me where the shaded area is, so I cannot answer the original question