So remember that a reflection is a rigid motion. It only moves the quadrilateral, it doesn't change its size at all, which includes the angles and side lengths as well.
Therefore, x-axis (and all) reflections preserve the congruency of the original image and the after image, and does not alter side lengths and angle degrees. The only thing it does is flip the image so that it's the same distance from the x-axis on the other side.
