Answer: 0.5
Explanation:
We know that the scale factor for dilation is the ratio of the side-length of the image to the side-length of the pre-image.
From the given figure, In Pre-image ΔABC , we have AC=18
In Pre-image ΔA'B'C', we have A'C'=9
Now, the scale factor will be :_

Now, the scale factor for this dilation = 0.5