I believe the area of the blank rectangle, the biggest one, is 2800. The whole rectangle all together is 3225.
Step-by-step explanation:
Since the length of one of the rectangles is 70, the rectangle with an area of 210 will have a side length of 3. This means the rectangle with an area of 15 has a side length of 5. That means the rectangle with an area of 200 has a side length of 40. Therefore, the blank rectangle has an area of 2800, as it's 2 side lengths are 70 and 40.