Answer:
20
Explanation:
The intersection of perpendicular bisectors is the circumcenter, so ...
... BG = AG = CG = 25 . . . . . the radius of the circumcircle
... 2x-15 = 25 . . . . . . substitute for BG
... 2x = 40 . . . . . add 15
... x = 20 . . . . . . divide by 2