Step-by-step answer:
Given an enlargement from preimage (ABC) to image (A'B'C').
Need to find scale factor.
Solution:
Scale factor = linear size of image / linear size of preimage.
From the accompanying diagram, we see that
L(preimage) = AC = 4 units
L(image) = A'C' = 12 units
Therefore
Scale factor = L(image) / L(preimage) = 12 / 4 = 3
