class MyClass { private $id; public function setId($newId) { $this->id = $newId; } public function getId() { return $this->id; } } $obj = new MyClass(); $obj->setId(123); echo $obj->getId(); // Output: 123In this example, we create a class called "MyClass" that has a private variable called "id". We then define a public method called "setId" that takes a parameter $newId and sets the value of the "id" variable to the new ID. We also define a method called "getId" that returns the value of the "id" variable. We then create an instance of the "MyClass" class and call the "setId" method with the value 123. We then output the value of the "id" variable using the "getId" method, which gives us the output "123". The package/library that the setId method belongs to depends on the context in which the method is being used. In our example, the setId method is part of the "MyClass" class that we defined. The package/library that this class belongs to would depend on how the class is being used and organized within the application or system.