Multiple "ifs" to base sequential numbering (automatically)... Need help!

I am trying to get an auto numbering formula to generate based on the following:
Field - Company (multiple choice) A or B

If Company is A, it then needs to decipher "operated by" K, C or U in order to assign the next PO number
numbering sequence ... 1000.00, 1000.01, 1000.02

K would be the next 1000.00
C would be the next 2000.00
U would be the next 4000.00
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then if Company is B, it would then just need to pull the next 5000.00 PO number as Company B doesn't matter the "operated by"

looking for this to automatically decipher whichever the next PO would be if following which choices/field information is placed within my Purchase Order table... is this something to build right in there or would I need sub tables to be able to have the multiple "if" work and pull the next PO accordingly. please help giving exact directive steps to follow!

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Jen Neall
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