Answer: y = 78
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Justification #1: Angle x is 78 degrees as these two angles are corresponding angles (congruent due to the parallel lines). We also know that y = x because they are vertical angles. So by the transitive property, y = 78
Justification #2: The parallel lines mean that the alternate exterior angles are congruent, so y = 78 through one step (instead of multiple steps in the prior justification)
