I have a table like this

A B C D E F
INVOICE# DATE NAME SALE Amount Rec/Deposit BALANCE
101 8/1 Mike $500 $200 $300
102 8/2 Mary $100 $100 0
103 8/3 John $200 $100 $100
..
..
9/1 Mike $300 0

When Mike comes in on 9/1 to pay off his $300 balance from invoice #101 on
8/1. I would like to record the payment and the fact the the balance for Mike
is now $0 on this spreadsheet.
How do I look up the balance for Mike? Either based on the invoice #, Name,
I don't care. Eventually the list will contain 100s of transactions so I
can't look it up manually


Please