I would like to know how to go about formulate a subtotal matching formula,

I looks like this;

first list with reference.

abcd
merchant date amt ref.
1234 06/01/09 500.00 1
1233 06/02/09 100.00 2
1233 06/02/09 100.00 3
1233 06/02/09 100.00 4
1233 06/02/09 100.00 5

second list w/o reference

abcd
merchant date amt ref.
1234 06/01/09 500.00 ?
1233 06/02/09 400.00 ?


need to fill in the "?"