Answer: 25
Reason:
The order of ABCD and EFGH is important. This is because the letters pair up based on their position.
D and H pair up because they're the last letters of ABCD and EFGH respectively. Similar polygons have congruent corresponding angles.
Take note of how the angles are marked to indicate which angles pair up.
D = H
4x = 100
x = 100/4
x = 25