First, let's take a look at the larger polygon. The topmost side is 7 units long. Now, let's look at the small polygon. The topmost side is 1 unit long.
These polygons differ by a scale factor of 1/7.
7 * (1/7) = 1
49 * (1/7) = 7
Now, we know that x = 7.
The larger polygon has side lengths of 7, 49, 7, 49
The smaller polygon has side lengths of 1, 7, 1, 7