public Price Convert(Price price)
        {
            // To perform a currency conversion, divide the local price by the conversion rate
            // and return a new price in the selling currency

            throw new NotImplementedException();
        }
        public Price Markup(Price price)
        {
            // To mark up a price, return a value equal to the current price
            // plus the proportion of the value indicated by PercentageRate

            throw new NotImplementedException();
        }
 public TourDeparture(int id, string description, DateTime departureDate, Price localCost)
 {
     Id = id;
     Description = description;
     DepartureDate = departureDate;
     LocalCost = localCost;
 }
 public TourDepartureSellingPrice(TourDeparture tourDeparture, Price sellingPrice)
 {
     TourDeparture = tourDeparture;
     SellingPrice = sellingPrice;
 }