We're multiplying each coordinate by 0.75, which is a value between 0 and 1. Whenever the scale factor is between 0 and 1, we always have a reduction. In this case, the linear dimensions are decreasing by 25% because 1-0.75 = 0.25 = 25%
So for instance, if the preimage had a side length of 12, then 0.75*12 = 9 is the corresponding image length. This is a reduction of 12-9 = 3. Then note how 3/12 = 0.25 = 25% is how much of a reduction we're dealing with.
