Let BF be x and AF be (8-x).

From the meaning of the question: 4? +x？ =(8-x)？

Solution: x=3

∴AF=8-3=5

In the era of △ABF and △,

AB = AG∠B =∠ Age

∠∠GAE+∠EAF = 90

∠BAF+∠EAF=90

∴∠GAE=∠BAF

∴△ABF is equal to △△ age (ASA).

∴S△AGE=3×4/2=6

AE = 5

∴GM=2S△AGE/AE= 12/5

ED = GE = BF = 3

∴S shadow =1/2× 3×12/5 =18/5.

So choose answer C.