The operator is 'sumif', which means add the number only if an indicator is set.

To do this, you need a way to tell Excel to add the number *only if Wal-Mart is the store.

1. Set an indicator for Wal-mart. Possibly something like add numbers if column g = w. the formula looks like this:

a1+SUMIF(c1,"w",b1)

=a1 (the Wal-mart total)
b1 the column containing the amount paid for this transaction
c1=the indicator. If not 'w', the sum will not happen.
Place the formula in a2, a3, and so on.
You can do that by pressing f5 for goto, and selecting something like a3_a20, then pasting a2 into a3.