File attributes are preventing file modification, which is causing the error message. The output

of lsattr /home/user/data.txt shows that the file has the immutable attribute (i) set, which means

that the file cannot be changed, deleted, or renamed. The command setfacl -b

/home/user/data.txt tries to remove the ACL from the file, but fails because of the immutable

attribute. The administrator needs to remove the immutable attribute first by using the

command chattr -i /home/user/data.txt and then try to remove the ACL again. The other options are

incorrect because they are not supported by the outputs. The administrator is using a highly

privileged account, as shown by the # prompt. The filesystem is mounted with the correct options, as

shown by the output of mount | grep /home. SELinux file context is not denying the ACL changes, as

shown by the output of ls -Z /home/user/data.txt. : CompTIA Linux+ (XK0-005) Certification Study

Guide, Chapter 11: Managing Files and Directories, pages 357-358.