3、　　友元编写C++程序完成以下功能：（1）　　定义一个Boat和Car两个类，他们都具有私用属性——重量；（2）　　编写一个函数，计算两者的重量和。double TotalWeight(Boat& b, Car& c) -Friend write C++ program perform the following functions: (1) the definition of a Boat and Car two classes, they have private property- Weight　(2) write a function to calculate the weight of both and. double TotalWeight (Boat &　b, Car &　c)