We pick b.root-servers.net, one of the 13 root servers (1), and ask it about joyfm.org and learn that org is delegated to six name servers (2), so we ask a2.org.afilias-nst.info where we learn that joyfm.org is delegated to two name servers, including ns1.bnt.com (3), so we ask that one and get the following answer: