Question

The scale factor of the dilation is...

Answer 1

The rule for dilation (about the origin) is
(x,y)->(kx,ky)  where k is the dilation factor.

Let's try a few points,
D(4,8)->D'(2,4)=((1/2)4,(1/2)8)  => k=1/2
F(8,8)->F'(4,4)=((1/2)8,(1/2)8) => k=1/2
We can repeat the same verification with points E & G with the same results, so
Answer: scale factor is 1/2, or 0.5.