Answer is 34 units.
Figures are defined by pre-image and image, so the image would be the dilation while the pre-image is the original figure. So with the preimage being larger, the dilation has to be a fraction less than 1.
Here preimage is smaller, and image is bigger hence scale factor is greater than 1 i.e. 2
Due to dilation, a similar figure is obtained without disturbing the shape of pre image.
Hence AB will becomes A'B' with length = scale factor x AB
= 2x AB.
We can find out AB using distance formula
AB = √(x₂-x₁)²+(y₂-y₁)²
=√(8-0)²+(8+7)²=√(64+225) =√289 = 17
Hence Length of A'B' = 2(17) = 34 units.