//Problem 19
        public static string GetSalesWithAppliedDiscount(CarDealerContext context)
        {
            var sb = new StringBuilder();

            var sales = context
                .Sales
                .Select(e => new ExportSalesWithAndWithoutDiscounts
                {
                    Car = new ExportCarDto
                    {
                        Make = e.Car.Make,
                        Model = e.Car.Model,
                        TravelledDistance = e.Car.TravelledDistance
                    },
                    Discount = Math.Truncate(e.Discount),
                    CustomerName = e.Customer.Name,
                    Price = e.Car.PartCars.Sum(pc => pc.Part.Price),
                    PriceWithDiscount = e.Car.PartCars.Sum(pc => pc.Part.Price) - e.Car.PartCars.Sum(pc => pc.Part.Price) * (e.Discount / 100m)
                })
                .ToArray();

           var xmlSerializer =
          new XmlSerializer(typeof(ExportSalesWithAndWithoutDiscounts[]),
          new XmlRootAttribute("sales"));

            var namespaces = new XmlSerializerNamespaces();
            namespaces.Add("", "");

            using (var writer = new StringWriter(sb))
            {
                xmlSerializer.Serialize(writer, sales, namespaces);
            }

            return sb.ToString().TrimEnd();
        }