I am using Excel 97.

I need to compare two different worksheets. The worksheets represent
daily sales activity. Column A in both worksheets represents the
customer ID, Column B is product description and Column C is sales
amount.

If the Customer ID (Column A) in yesterday's data appears again in
today's worksheet, I am to compare the sales (Column C ). I am to
substract yesterday's sales from today sales. The new report is to
appear in another worksheet like the example below.

Customer ID Item Description Sales

1 Bonds $1,000,000
2 Stocks ($100,000)

Any ideas how to approach this problem.