sql help-select sum of 2 fields in flat file

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Trying to select data from flat s36 file (and that is working)
dynamically building string (rpgsql)
select from ardtl where substr(F00001,22,5) = x'000015679F'
the 22,5 is a packed field in the flat file

now need to select based on the sum of 2 packed fields in a record.
(ar invoice amt + ar paid).
How do I build a select based on sum of 2 fields.
Every sql book & tutorial i see is to "simple" for this.

thanks in advance
jim franz
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