In a circle, the internal vertical angles have a formula of 
In this case, the formula would be:
We know that whole circle is 12x. And 12x is equal to 360°. When we put that into equation:
If x is 30°:
So, angle 7 is 90°.
In this case, the formula would be:
We know that whole circle is 12x. And 12x is equal to 360°. When we put that into equation:
If x is 30°:
So, angle 7 is 90°.