<span>If an image of a triangle is congruent to the pre-image, then the scale factor of the dilation must be n = 1. Dilating an image with a dilation factor of 1 will result to the same image and that ensures the congruency between the pre-image and the dilated image.</span>
if you go from the slant height, the path is shorter to the top, since the hypotenuse is the longest of all sides in a right-triangle.
that said, is shorter but is also steeper, so the lateral edge is longer but less steep and thus a bit simpler though longer, but we're only asked on which is shorter.