We have a line:
And we draw its perpendicular bisector:
Then, any point on the bisector is equidistant to the endpoints of the line:
This is called: the perpendicular bisector theorem.
In this case we have that:
Since the line is the black one, the bisector is the purple one, then both red segments measure the same : 9.
Answer: BG = 9 (bisector theorem)
In this case, as we can observe in the image, the red lines are equidistant then CG = 10
Answer: CG = 10 (bisector theorem)