if the square rug has a side length of 6, we can say that the area of the rug is 36 ft²
since the inner square has an area 25% of the rug's area, you multiply 36 by 0.25 to get 9 ft²
since we know that the area of the inner square is 9 ft², we can find the length of the inner square since x²=9 ft².
x=3 ft