Answer:
138 degrees
Step-by-step explanation:
Since angles B and C are supplementary, that would mean they add up to 180. The problem tells us that angle C is 42 degrees, so that would mean that angle B is 138 degrees. We are also told that angles A and B are vertical, which would mean that they are congruent to each other. That leaves us with the answer that angle A is 138 degrees.
Hope this helps! :)
