So you question is most likely about a triangle DEF with the 3 angles being named D, E, F. The triangle would look something like the image attached below.
If that is what is being asked then i need more info to answer but
By Definition it would be 180 degrees.
Answer:

Step-by-step explanation:
Using the section formula
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=
=
= 
Answer:
88
Step-by-step explanation:
Answer:
D, B, C, and B
Step-by-step explanation:
I just did it