The center of rotation of this figure is point G and it is a rotation of 90 degrees. This is a rotation of 90 degrees because if you connect point A of the pre-image to point G and then connect point G to A' of the image, this angle is 90 degrees. This is also the case with all other points of my image. Each vertex also goes the same direction around the center of rotation. Each vertex is also the same distance away from the center of rotation, or point G, a crucial part into forming a rotation.

Information: Rotations