I seriously need help with this question!! I'm not kidding! Please help me!!

Answer:
63
Step-by-step explanation:
The two tangents to a circle from the same point are the same length.
SD = SG
5x +18 = 8x -9
27 = 3x . . . . . . . . add 9-5x
9 = x . . . . . . . . . . divide by 3
SG = 8x -9 = 8·9 -9
SG = 63