20. A smaller rectangle is centered within a larger rectangle such that the shaded area is created as shown below. The dimensions of both rectangles are shown in terms of x.
i don´t know how to solve this
![20 A smaller rectangle is centered within a larger rectangle such that the shaded area is created as shown below The dimensions of both rectangles are shown in class=](https://us-static.z-dn.net/files/dec/63eef71aacc75c719909a017e4f4c97b.png)