Does any one mind helping me on this question I have struggle solving it

Which representation has a constant of variation of -2.5

(05.08a)triangle abc is transformed to similar triangle a′b′c′ below: a coordinate plane is shown. triangle abc has vertices a at 2 comma 6, b at 2 comma 4, and c at 4 comma 4. triangle a prime b prime c prime has vertices a prime at 1 comma 3, b prime at 1 comma 2, and c prime at 2 comma 2. what is the scale factor of dilation? 1 over 2 1 over 3 1 over 4 1 over 5

What are the coordinates of the point that is 1/3 of the way from a to b? a (2,-3) b (2,6)