What is the justification for the congruent proof that the measure of angle A + the measure of angle B=180?

Question

I'm doing one-step proofs. I have a picture of 2 angles: angle A and angle B. I need the conclusions and the justifications to prove that angle A + angle B equals 180.

Answer 1

Only reason that I can think of if from a point of intersection , center point, draw any circle the central angle inscribed of a straight has opposite arc of 180°.

  Half of a full revolution will intersect the circle along diameter with a central angle congruent to

 

   360°/ 2= 180°