A retailer classifies accounts as having one of four possible states. "paid up," "overdue at most 30 days," "overdue less than 60 days but more than 30 days," and "bad." If no payment is made on an overdue account by the end of the month, the status moves to the next state. When a partial payment is made on an overdue account, its improved status depends on the size of the payment. The matrix on the right describes the changes in status of accounts. Paid $30