Hilda and Tim Piwek own Campus Fashions. From its inception, Campus Fashions has sold merchandise on either a cash or credit basis, but no credit cards have been accepted. During the past several months, the Piweks have begun to question their sales policies. First, they have lost some sales because of refusing to accept credit cards. Second, representatives of two metropolitan banks have been persuasive in almost convincing them to accept their national credit cards. One bank, City National Bank, has stated that its credit card fee is 4%.

The Piweks decide that they should determine the cost of carrying their own credit sales. From the accounting records of the past 3 years, they accumulate the following data (amounts in thousands).