A note about the images: each image shows approximately the same physical area on each planet or moon - about 360km x 360km. The images themselves are different sizes because they are do not all have the same resolution, so some of the images are larger in a pixel-by-pixel size. The bottom line: don't worry that the images are not the same size in pixels.
On your homework, describe how you decided which surfaces were older and younger. Then make the assumption that the oldest surface is as old as the solar system: 4.5 billion years. With that assumption, how old are the youngest two surfaces? Explain how you determined this.