28.9 A large New England lumber producer, Salisbury Stakes, Inc., is planning to use a lockbox system to speed collections from its customers located in the midwestern United States. A Chicago-area bank will provide this service for an annual fee of $15,000 plus

$0.25 per transaction. The estimated reduction in collection and processing time is two days. Treasury bills are currently yielding 6 percent per year.

If the average customer payment in this region is $4,500, how many customers each day, on average, must use the system to make it profitable?