<span>Here's the rule. I'm SURE you learned it in Middle School. Or, I guess I should say: I'm SURE it was taught in Middle School.
Vertical angles are equal.
"Vertical angles" are the pair of angles that don't share a side, formed by two intersecting lines.
AND ... even if you forgot it since hearing it in Middle School, it was clearly explained in the answer to the question that you posted 9 minutes before this one.
In #8, 'x' and 'z' are vertical angles. 'y' and 116° are vertical angles.
In #9, 'B' and 131° are vertical angles.
In #10, 'B' and 135° are vertical angles.
For all of these, it'll also help you to remember that all the angles on one side of any straight line add up to 180°. </span>
You are right to circle both 10 or 12. Neither can be solved without knowing something about the x values in 10 and the x value of the smaller base in 12.
