Using the concepts of straight angle, ∠DFC = 80°.
What is a straight angle?
A straight angle is an angle equal to 180 degrees. It is called straight because it appears as a straight line.
Since AD is a straight line.
∠AFE + ∠EFD = 180°
125° + ∠EFD = 180°
∠EFD = 180° - 125° = 55°
Now, EB is a straight line.
∠EFD + ∠DFC + ∠CFB = 180°
55° + ∠DFC + 45° = 180°
∠DFC = 180° - 100° = 80°
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