x = 7 or x = 17
Basically, if you draw this out on a grid you will get three lines. All you need to do is find the distance from y=9 and y=4, which is 5 units. Since squares have all equal sides, you have to create a line that will enclose the shape in 5 units. You can either place it +5 or - 5 units in the x-coordinate from x=12.
