text: #ifndef QUOTE_HPP
  #define QUOTE_HPP
  
  #include <iostream>
  #include <string>
  
  class Quote {
   public:
    Quote() = default;
    Quote(const std::string& bookNo, double price) : mBookNo(bookNo), mPrice(price) {}
  
    std::string isbn() const;
    virtual double net_price(size_t n) const;
  
    virtual ~Quote() = default;
  
   private:
    std::string mBookNo;
  
   protected:
    double mPrice;
  };
  
  static double printTotal(std::ostream& os, const Quote& quote, size_t n) {
      double res = quote.net_price(n);
      os << "ISBN: " << quote.isbn() << " # sold: " << n << " total due: " << res << '\n';
  
      return res;
  }
  
  #endif
  