Dojo: Who's on the List but Gone

Two sorted rosters: /root/all-users.txt is every account ever provisioned; /root/active-users.txt is who's still active. In ONE line, print the usernames that appear in all-users but NOT in active-users (the departed accounts) and write them to /root/answer.txt.

This is a set difference on two already-sorted files — the classic job of comm. Suppress the columns you don't want.