Solution Review: Polymorphism

<?php 
abstract class User {
    protected $scores = 0; 
    protected $numberOfArticles = 0;
    public function setNumberOfArticles($int) {
        $numberOfArticles = (int)$int;
        $this -> numberOfArticles = $numberOfArticles;
    }
    public function getNumberOfArticles() {
        return $this -> numberOfArticles; 
    }
    abstract public function calcScores();
}
class Author extends User { 
    public function calcScores() {
        return $this -> scores = $this -> numberOfArticles * 10 + 20;
    } 
}
class Editor extends User {
    public function calcScores() {
        return $this -> scores = $this -> numberOfArticles * 6 + 15;
    } 
}
function test()
{
  $author1 = new Author();
  $author1 -> setNumberOfArticles(8); 
  $editor1 = new Editor();
  $editor1 -> setNumberOfArticles(15); 
  
  return "Author score is " . $author1 -> calcScores(). " and Editor score is " . $editor1 -> calcScores();
}
echo test();
?>