According the following requirements to create a local directory /common/admin.
• This directory has admin group.
• This directory has read, write and execute permissions for all admin group members.
• Other groups and users don’t have any permissions.
• All the documents or directories created in the/common/admin are automatically inherit the admin group.
A. See explanation below.
Exploding the last command:
mkdir -p /common/admin
chgrp admin /common/admin
chmod g+rwx /common/admin
chmod o=— /common/admin
chmod g+s /common/admin