Answer:
50 degrees
Explanation:
Theorem: The angle subtended by the diameter is a right angle.
By the Circle Theorem above, the angle at F is a right angle and thus Triangle EGF is a Right Triangle.
We are to determine the measure of GF.
|GE|=|GO|+|OE|=10+10=20 Inch
Using Trigonometry in the second triangle attached

Theorem: Angle at the centre is twice the angle at the circumference.
By the theorem above:
Measure of Arc GF = 2 X

=2 X 25
mGF=50 degrees
Therefore, the measure of GF is 50 degrees (to the nearest degree)