Reflection is an example of transformation in which a given image is flipped over a reference line which changes the orientation of the figure, but not its length and shape. A rotational transformation is formed by two reflections.
In the given question, image ABCD is reflected over lines I, then m at an angle of 51° to each other. Since rotation is twice the acute angle with respect to the center of rotation, therefore ABCD rotates through an angle of 102°.
