public class CartItem { public CartItem() {} public CartItem(Product product, int quantity) { this.Product = product; this.Quantity = quantity; } public Product Product { get; set; } public int Quantity { get; set; } public void AddQuantity(int quantity) { this.Quantity += quantity; } public string Display() { string displayString = Product.productName + " (" + Quantity.ToString() + " at " + Product.listPrice.ToString("c") + " each)"; return displayString; } }