Answer is 2/3 scale factor
Step by step
Divide the side of the image by the pre image.
Side x’ y’ is 12
Side x y is 18
12/18 simplified to 2/3
Check your work
Side x w = 12
12 * 2/3 = 8
x w is congruent to y z
So y’ z’ is 8 so they are the same after the dilation
So your answer is correct