Look at the lines below and write down the correct answer.
AB = cm;
CD = cm;
AB + CD = cm.
AB = 3 cm.
The starting point of line CD is 4 and the end point is 9. 9 cm 4 cm = 5 cm. So the length is 5 cm.
The total length AB + CD = 3 cm + 5 cm = 8 cm.