When a dilation is performed, the scale factor can be found as the quotient between the lengths of two corresponding parts of the scaled figure and the original figure.
In this case, notice that the side AB in the original figure corresponds to the side A'B' in the scaled figure.
Then, the scale factor is the quotient of the length A'B' over the length AB.
Since A'B' = 3 and AB = 1, then the scale factor is equal to:
Therefore, the scale factor is equal to 3.