Contribution #636

Problem: ru/8.4.2

Added 8.4.2 8.4.4 8.4.5 8.4.15 8.4.19-8.4.21

Editor: Aliaksandr Melnichenka ( @astrosander )

Time: November 18, 2023 at 08:42 PM

GitHub commit: 269282145273f7c4e9db57a1fc62d534b49c2c58

+239 -48 lines changed