Answer is 1/2 scale factor
Step by step
Measure sides of pre image ABCD and image A’B’C’D’ lines from graph
Measure of
Pre Image line AD = 8 units
Image Line A’D’ = 4 units
Divide image by pre image
4/8 = 1/2 scale factor
Pre image line BC = 4 units
Image line B’C’ = 2 units
Divide image by pre image
2/4 = 1/2 scale factor
Keep in mind your pre image is bigger and your image is smaller so your scale factor will be less than one, or a fraction.