The reflection on the left (known as the pre-image) has dimensions clearly given, while the shape on the right (known as the image) has no dimensions given but, a careful observation shows that the scale factor is the same, that is, 1 : 1.
This means the sides and angles do not change value(s). The image simply lies in a different location, that is, a different quadrant. The shape, the size and the orientation has not changed which means the dimensions in the image is the same as the pre-image.