To solve this problem you must apply the proccedure shown below:
 1. You have the following information given in the problem above:
 -  The room has square dimensions and it has been built with two pieces of sheetrock, a smaller one and a larger one.
 2. Therefore, let's call
 x: the smaller one.
 y: the larger one.
 3. Then, you have that the lenght of the wall is the sum of the smaller one and the larger one:
 x+y
 4. So, the area of the room is:
 (x+y)(x+y)
 (x+y)²
 Therefore, the answer is: (x+y)²