If you look at the diagram, you can see that the length of rectangles A and B are the same, and are also the same as they were in the original square. We can find the length of each side by finding the square root of the area of the square to give us the length and width of the square which is 9. Now that we know that the length of both rectangles A and B, we can find the width of both rectangles by taking 9, and splitting it into 3 portions of 3. Since the ratio of area is 2:1, we could also do this with the area, but since we know the lengths are the same, we know the widths are proportional to the area. Using the ratio of 2:1, and the 3 portions of 3, you can combine 2 of these portions to get 6, and since the ratio 6:3 is proportional to 2:1, these measurements can be used as the width of each rectangle. Thus, the answer given above.
