php - Constructor argument not inheriting down to children? -

i new php , in particular oop. have piece of test code thought return:

what result?8 result?8 

but, instead getting:

what result?5 result?8 

the arguments passed instance of class seem not getting assigned x. have tried echo $second->x returns nothing.

have got code wrong, misunderstanding inheritance or misunderstanding constructors?

here code:

<?php class first{     public function __construct($x){         $this->x = $x;         echo "what result?";     } }                                      class second extends first{     public function calculation(){         $z=5;         return $x+$z."<br />";     } }  class third extends first{     public function calculation(){         $z=5;         $x=3;         $y=$x+$z;         return $y."<br/>";     } }  $second = new second('3'); echo $second->calculation(); $third = new third('3'); echo $third->calculation(); ?> 

just little updation on within second class

class second extends test{     public function calculation(){         $z=5;         return $this->x+$z."<br />";//$x  should $this->x     } } 

output:

what result?8 result?8