Answer: x = 35 (choice D)
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Work Shown:
secant angle = (far arc - near arc)/2
angle BGC = (arc BC - arc AD)/2
40 = (115 - x)/2
2*40 = 115-x
80 = 115-x
115-x = 80
-x = 80-115
-x = -35
x = 35
For more information, you can search out "secant angles" and it should go over how the formula is set up and why it works.