angles 5 and 1 are vertical angles. i'm not exactly sure how to explain this.
here is a site that may explain the relationships between angles with a transversal better:
https://tutors.com/math-tutors/geometry-help/types-of-angle-relationships#:~:text=When%20two%20parallel%20lines%20are%20intersected%20by%20a,all%20the%20types%20of%20angle%20relationships.%20Congruent%20Angles
hope this helped! i strongly recommend that you check out the site i linked above. if you have any other questions about this, feel free to ask !