You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: structs3.rs
    path of file: ./repos/rust-course/assets/rustlings-zh/exercises/structs
    
    the code of the file until where you have to start completion: // structs3.rs
// 接口既可以包含数据也可以处理逻辑。
// 在这个练习中，我们已经定义了 Package 结构，但我们想测试一些根据它实现的逻辑。
// 让代码通过编译和测试！
// 如果你有问题，可以执行 `rustlings hint structs3` 查看提示

// I AM N
    
    fn calculate_transport_fees() {// 译：计算运输费
        let sender_country = String::from("Spain");
        let recipient_country = String::from("Spain");

        let cents_per_gram = 3;// 译：分/克（一克需要多少分钱）

        let package = Package::new(sender_country, recipient_country, 1500);

        assert_eq!(package.get_fees(cents_per_gram), 4500);
    }