public decimal CalculateDiscount(OrderItem orderItem)
 {
     decimal discount = 0;
     if (orderItem.CalculatePartialTotal() >= 100)
     {
         discount = orderItem.CalculatePartialTotal() * 10 / 100;
     }
     return discount;
 }
 public decimal CalculateDiscount(OrderItem orderItem)
 {
     return orderItem.CalculatePartialTotal() * 15 / 100;
 }