Answer:
x = 13
Explanation:
The relevant fact about vertical angles is that they are congruent, their measures are equal. This lets you write an equation relating the expressions for the measures of angles A and B.
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∠A = ∠B
(8x -12)° = (6x +14)° . . . . . substitute given expressions
2x = 26 . . . . . . . . . . . divide by °, add 12-6x
x = 13 . . . . . . . . . . divide by 2