php面向对象编程，这两个题目代码怎么写？

题主要的代码如下

<meta charset="utf-8">
<?php
    class Book{
       private $bookName;
       private $author;
       private $price;
       
       public function __construct($bookName,$author,$price){
           $this->bookName=$bookName;
           $this->author=$author;
           $this->price=$price;
       }
       function __set($property_name, $value) { 
           $this->$property_name = $value;
       }
       function __get($property_name) {
           return isset($this->$property_name) ? $this->$property_name : null;
       }
       public function __destruct(){
           //echo '------这里是析构函数------<br>';
       }
       public function displayBook(){
          echo "书名：".$this->bookName;
          echo "<br>作者：".$this->author;
          echo "<br>价格：".$this->price;
       }
    }

    $book=new Book("高数","未知",120);
    $book->displayBook();
    $book->bookName="abcdefg";
    echo "<br>";
    $book->displayBook();
?>

有帮助麻烦点下【采纳该答案】