bar.php

<?php

class bar extends Foo
{
    public function hello($name, $surname)
    {
        echo "hello";
    }
}

?>

Foo.php

<?php

class Foo
{
    public function hello($name)
    {
        echo "hello".$name;
    }
    
    public function sayWhat()
    {
        echo $foo;
    }
}