What’s the scale factor? Please hurry I’m tired and sleep deprived help me I just don’t get it and I want sleep

In order to find the scale factor we begin by selecting one pair of corresponding sides.
Selecting the base of the triangle
Base of triangle AC is 3 units.
Base of triangle (AC)' is 7.5 units
According to the proportion
[tex]AB\cdot k=(AB)^{\prime}[/tex]REPLACE TH