The answer is D.
The first one says you add -4 each time in the sequence.
The second says you add -2 each time in the sequence.
The third says you multiply by -2 each time in the sequence.
The fourth says you multiply by -4 each time in the sequence.
-2*-4=8
8*-4=-32
To solve this you need to know Pythagorean theorem.
First, EG is 24, so the halfway points are 12. Knowing Pythagorean triples, you can use 5,12,13 and 12,16,20.
DF = 5+16
DF = 21
If you don't know Pythagorean triples, I have worked it out on the image attached.