Question 186075
I am sorry that no one has answered you question. I hope I am able to. 
It says that A is the center of a line drawn from B & C. 
B---------A---------C
Then is says that D is the center of the line between A & C. 
B---------A-----D----C
The last one says that E is the center of the line between A & D.
B---------A---E---D----C
The line between E & D is 2 units in length. With that said:
B---------A---E---D----C
     8      2   2    4
So if the length of line between A & C is 8 units then the line between B & A is also 8 units.

8 + 8= 16 units for the entire line (B & C)

I hope I was able to answer your question.