One region on the moon is covered with craters, while another is a smooth volcanic plain. which is older? how do we know?

6.4 One region on the Moon is covered with craters, while another is a smooth volcanic plane. Which is older? How much older? How do we know? The crater-covered surface is close to the same age as theMoon is - about 4 billion years. ... enshrouded in clouds, how do we know as much as we do about its surface?

Here is a picture  of the net. its 4 squares in a row diagonal and on the third draw one square aove and under