The measure of the two vertical angles is 15°
The two vertical angles have measures (4x-21)° and (x+6)°
Note that:
The measure of two vertical angles are equal
Therefore, equate (4x-21)° and (x+6)° and solve for x
(4x-21)° = (x+6)°
4x - 21 = x + 6
Collect like terms
4x - x = 6 + 21
3x = 27
x = 27/3
x = 9
Substitute x = 9 into 4x - 21
4x - 21 = 4(9) - 21
4x - 21 = 15°
Substitute x = 9 into x + 6
x + 6 = 9 + 6
x + 6 = 15°
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