Answer
Find out the length of line segment GF .
To prove
In Δ GEF is a right triangle .
As shown in the diagram
GE = 10 units
EC = 7.5 units
By using the pythagorean theorem
Hypotenuse² = Perpendicular² + Base²
GC² = GE² + EC²
   =  10² + 7.5²
   = 100 + 56.25
   = 156 .25
GC = 12 .5 units
As shown in the diagram
CF is the radius of a circle .
CF = 7.5 units (As in the figure EC = 7.5 units)
GF = GC + CF
    =  12 .5 units + 7.5 units
   =  20 units
Therefore option (d) is correct .
Hence proved