The answer is C. 180°
Step-by-step explanation:
This page explains you thoroughly how it works. https://www.khanacademy.org/math/geometry/hs-geo-congruence/hs-geo-congruence-theorems/v/proof-sum-of-measures-of-angles-in-a-triangle-are-180#:~:text=Learn%20the%20formal%20proof%20that,triangle%20sum%20to%20180%C2%B0.