Problem
1. Real cash registers can handle both bills and coins. Design a single class that expresses the commonality of these concepts. Redesign the Cash Register class and provide a method for entering payments that are described by your class. Your primary challenge is to come up with a good name for this class.
2. Enhance the invoice-printing program by providing for two kinds of line items: One kind describes products that are purchased in certain numerical quantities (such as "3 toasters"), another describes a fixed charge (such as "shipping: $5.00").