Whitlock Department Stores runs a multiuser DBMS on a LAN file server. Unfortunately, at the present time, the DBMS does not enforce concurrency control. One Whitlock customer had a balance due of $500.00 when the following three transactions related to this customer were processed at about the same time:

• Payment of $500.00

• Purchase on credit of $100.00

• Merchandise return (credit) of $50.00

Each of the three transactions read the customer record when the balance was $500.00 (i.e., before any of the other transactions were completed). The updated customer record was returned to the database in the order shown in the bulleted list above.

a. What balance will be included for the customer after the last transaction was completed?

b. What balance should be included for the customer after the three transactions have been processed?