How to extract .rar files on ubuntu / Install 7zip on ubuntu

1. First of all, open your terminal emulaotr on your ubuntu OS (press Ctrl + Alt + T)
2. Type (for extract unrar files with unrar apps)
   

   "sudo apt-get install unrar-free" and press 'Enter' button to confirm

   Type (for extract unrar files with 7zip apps, or zipping/extracting any files)
   

   "sudo apt-get install p7zip-full" and press 'Enter' button to confirm

   
   And you can try to extract now.. 
   Good luck.. ;-)
   You can comments if you have a problem with that..