We pick f.root-servers.net, one of the 13 root servers (1), and ask it about 68.132.137.in-addr.arpa and learn that in-addr.arpa is delegated to six name servers (2), so we ask e.in-addr-servers.arpa where we learn that 137.in-addr.arpa is delegated to eight name servers, including x.arin.net (3), so we ask that one and learn that 132.137.in-addr.arpa is delegated to four name servers (4), so we ask dnssec2.singnet.com.sg and learn that 68.132.137.in-addr.arpa is delegated to two name servers (5), so we ask nuscc.nus.edu.sg and get the following answer: