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Answer:
C. 207°
Explanation:
Points D and F divide the circle into two arcs. The short arc is referred to by its end point: arc DF. The long arc has the same end points, so is referred to using a third point somewhere on the arc. That point is G.
Together, arcs DF and DGF make the complete circle, or 360°. The measure of long arc DGF can be found from that fact:
DF +DGF = 360°
153° +DGF = 360° . . . . substitute the given value for arc DF
DGF = 360° - 153°
arc DGF = 207°
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Additional comment
The tangents and external angle are completely irrelevant to the question asked by this problem.