Because line BD goes through the center of the circle Angle A is a right angle which equals 90 degrees.
Set the equation for A to equal 90 and solve for x:
3x-6 = 90
Add 6 to each side:
3x = 96
Divide both sides by 3:
x = 32
Now we have a value for x , use that to solve for angle b:
B = x +9 = 32 + 9 = 41 degrees.
Now we know A and B, we can solve for D.
The three inside angles of a triangle need to equal 180.
D = 180 - 90 - 41 = 49 degrees.
The answer is D) 49