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Explanation:
Place point F on line AB such that it is to the left of point A. In other words, point A is between points F and B.
Angle CAB is 105 degrees, so this makes angle CAF to be 75 degrees. This is because 105+75 = 180. The two angles are a linear pair.
Angle CAF is the angle formed between the tangent line AB and the chord segment AC.
Due to the tangent-chord theorem, inscribed angle CEA is also 75 degrees. Note how this inscribed angle subtends the arc cut off by the chord.
The inscribed angle theorem says we can double that inscribed angle to get 2*75 = 150, which is the measure of minor arc AC.
Arc CEA is therefore 360-(minor arc AC) = 360-150 = 210 degrees