Answer:
x = 6
Explanation:
Vertical angels are always equal, there fore angle A = angle B.
If angle A = angle B, and
angle A = 3x - 9 and angle B = x + 3, then
3x - 9 = x + 3
Now you can solve this like a regular inequality
Start by subtracting x by it's self then 3x to get both variables on one side.
2x - 9 = 3
Now you can add 9 to it's self and to 3 on the other side.
2x = 12
Finally, divide 2 by it's self and 12.
x = 6