I don't have a clue what she meant
Nor do i. . .
Can you talk with others who have the same homework assignment? What is the class currently working on in jcl (utilities like iebgener or idcams or filke-aid or sort)? Any reason given why the "fixed decimal" numbers cannot be at the end of the file (i too do not put such things at the beginning of the record)?
It may be time to ask for a clarificaton for the class if none of the others understand what is supposed to be done either.