Hey there! I'm happy to help!
The two letters of the line segment describe the end points, or the points that the line is in between.
We want to find the distance between E and F. The distance between D and E is 9, while the distance between D and F is 11. We see that from D to F is 2 more than D to E, which must mean that the distance between E and F is 2.
The length of EF is 2.
Have a wonderful day! :D
