Access: Need to sum multiple fields in single row when related field are equal

You're making this more complicated than it needs to be because your table design is not correct. You are "committing spreadsheet" - a venial sin for which the penance is studying normalization :-{)

A better table design would be to recognize that you have a classic many to many relationship between whatever your main table's Entity is and Ltrs - each main table entity seems to have zero, one, two, three or four (or more?) Ltrs, and each Ltr may pertain to zero, one, two or many Rows. The proper design for this has THREE tables:

ParentEntity

   EntityID (primary key)

   (other information about the entity as a thing in its own right)

Letters

  Letter (text primary key, or more likely two fields, an Autonumber PK and a letter, since I suspect you've simplified the example)

Amounts

   AmountID (autonumber primary key)

   EntityID (Long Integer, link to ParentEntity)

   Letter (or LetterID, link to Letters0

   Amt

Then instead of summing several FIELDS you can use a Totals query (or, as suggested, a Crosstab) to sum several RECORDS.

If I'm misinterpreting or oversimplifying your situation, please post the actual table structures; if that would reveal proprietary information, you can obfuscate the fieldnames - but don't distort it too much or we may not be able to understand the actual problem!

Base upon your table structure you can use a 'Crosstab' query.

If you need more assistance then post the SQL of the query you now have.