IOrderService orderService = new OrderService(); Order order = new Order { OrderId = 123, ProductId = 456, Quantity = 1 }; Customer customer = new Customer { FirstName = "John", LastName = "Doe" }; orderService.Add(order, customer);In this example, we're adding a new order with an ID of 123, a product ID of 456, and a quantity of 1. We're also associating this order with a new customer named John Doe. Package Library: It's difficult to determine the package library without more context about the code example and the specific implementation of the IOrderService interface. However, it's possible that the IOrderService interface is part of a custom service layer or business logic library created specifically for the project. Alternatively, it could be part of a larger ecommerce or inventory management library.