User “ahmed” owns a directory, “stuff,” containing a text file called “ourstuff.txt” that he shares with users belonging to the group “staff.” Those users may read and change this file, but not delete it. They may not add other files to the directory. Others may neither read nor write or execute anything in “stuff.” What would appropriate ownerships and permissions for both the directory “stuff” and the file “ourstuff.txt” look like?