Adding virtual keyword in front of get_price() in Hotel Room is enough.

class HotelRoom { public: HotelRoom(int bedrooms, int bathrooms) : bedrooms_(bedrooms), bathrooms_(bathrooms) {}

virtual int get_price() {
    return 50*bedrooms_ + 100*bathrooms_;
}

private: int bedrooms_; int bathrooms_; };

class HotelApartment : public HotelRoom { public: HotelApartment(int bedrooms, int bathrooms) : HotelRoom(bedrooms, bathrooms) {}

virtual int get_price() override{
    return HotelRoom::get_price() + 100;
}

};