<?php
class Box {
    protected  $_length;
    protected  $_width;
    protected  $_height;
    public function __construct($length, $width, $height) {
       $this->_length = $length;
       $this->_width = $width;
       $this->_height = $height;
    }
    public function volume() {
      return $this->_length * $this->_width * $this->_height;
    }
}
$myBox = new Box(20,10, 5);
$myVolume = $myBox->volume();
echo("Volume = " . $myVolume . "<br/>");
class Parcel extends Box {
     private $_deliveryAddress;
     private $_weight;
     public function __construct($length, $width, $height, $deliveryAddress, $weight) {
          parent::__construct($length, $width, $height);
          $this->_deliveryAddress = $deliveryAddress;
          $this->_weight = $weight;
     }
     public function cost() {
          $volume = $this->volume();
          if ($volume <= 200)
          {
              return 5;
          }
          else
          {
              return 10;
          }
     }
}
$myParcel = new Parcel(20,10, 5, '10 Bristol Road', '210');
$myCost = $myParcel->cost();
$myVolume = $myBox->volume();
echo("Volume = " . $myVolume . " Cost = " . $myCost . "<br/>");
?>