public interface IPriceInfo 

class MyPage : System.Web.UI.Page
{
   private double _VAT;
   private double _VATPercent = 0.0;
   private double _PriceWithVAT = 0.0;
   private double _PriceWithoutVAT = 0.0;
   private Dynamicweb.eCommerce.International.Currency _Currency = Dynamicweb.eCommerce.Common.Context.Currency;

   public virtual double VAT
   {
       get { return _VAT; }
       set { _VAT = value; }
   }

   public virtual double PriceWithoutVAT
   {
       get { return _PriceWithoutVAT; }
       set { _PriceWithoutVAT = value; }
   }

   public virtual double PriceWithVAT
   {
       get { return _PriceWithVAT; }
       set { _PriceWithVAT = value; }
   }

   public Dynamicweb.eCommerce.International.Currency Currency
   {
       get { return _Currency; }
       set { _Currency = value; }
   }


   public Dynamicweb.eCommerce.Prices.PriceInfo Substract(Dynamicweb.eCommerce.Prices.IPriceInfo info)
   {
       if (Currency.Code != info.Currency.Code)
       {
           throw new Dynamicweb.eCommerce.Prices.PriceInfoCurrencyException();
       }
       Dynamicweb.eCommerce.Prices.PriceInfo resinfo = new Dynamicweb.eCommerce.Prices.PriceInfo();
       resinfo.PriceWithVAT = _PriceWithVAT - info.PriceWithVAT;
       resinfo.PriceWithoutVAT = _PriceWithoutVAT - info.PriceWithoutVAT;
       resinfo.VAT = _VAT - info.VAT;
       resinfo.VATPercent = (resinfo.VAT / resinfo.PriceWithoutVAT) * 100;
       resinfo.Currency = Currency;
       return resinfo;
   }
}