Check the picture below.
the lengths of the corresponding horizontal lines is the same on each figure, 4 and 1.
the slope in red is the same for both figures, and the slope in yellow is the same on each figure, meaning the slanted sides on each figure is also the same length.
so the lengths in each figure is the same and the angles are also the same, so the shapes are congruent, and since they're congruent the scale factor will simply be 1 to 1 or 1:1, since neither is smaller or larger than the other.
