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Dear visitor !
Let read your post together.
The problem says that there is the telephone cable from A to D.
Notice that the problem says about ONE cable --- not about some set of cables.
Next, the problem tells us about different parts of this cable
- from A to B has the length of 103 yd.
- from B to C has the length of 72 yd.
- from C to D has the length of 51 yd.
Should I continue ?
It seems to me that at this point any, every and each person with a bit of common sense in his mind just knows how to get answer.
Simply add the three given numbers.
What else you can do with them ?
Have a good rest after reading my post (!)
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Your description of the cable placement on the plane was very picturesque.