B$+$ tree index with Alternative $2$ for data entries. un

Has $4$ levels $($the root, index level $1..)$

The order $60($minimum $60$ index and maximum $120$ index entries$)$

A search value k has at most $1000$ records and each disk page contains at most $50$ data records

If the B$+$tree is unclustered, what is the maximum I$/$O cost to retrieve the data records matching the search key value k