Using the definition of vertical angles, the value of z is: 15.
<h3>Vertical Angles Pair</h3>
The two pairs of opposite angles formed when two straight lines intersect are called vertical angles, and are therefore congruent to each other.
Thus:
2z + 10 = 40
2z = 40 - 10
2z = 30
z = 30/2
z = 15
Therefore, using the definition of vertical angles, the value of z is: 15.
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