Newbie Report/Sort Problem/Question

[hfcoverlover]

I'm a hobbiest using Access to save my First Day Cover collection in a data base. Nearly 10,000 items so far. The key to the collection is the "Scott Number", which I set up as a concatenation of three fields: Prefix as text, Number as number and Suffix as text. I want to sort on the Number field first when the Prefix is Null, next on the Prefix field. The underlying query sorts as desired. I've juggled the sort fields in the query and report but can't get the desired report output. Got code?
Thanks, Don