private function calculateShipping($shipping_option)
 {
     $numDisks = 0;
     $shippingCharge = 0.0;
     $itemCount = OrdersController::getCountOfItems();
     if ($shipping_option == 'ship_separately') {
         $shippingCharge += OrdersController::calculateShippingFee($itemCount['CD']['count']);
         $shippingCharge += OrdersController::calculateShippingFee($itemCount['DVD']['count']);
     } else {
         switch ($shipping_option) {
             case 'ship_together':
                 $numDisks = $itemCount['CD']['count'] + $itemCount['DVD']['count'];
                 break;
             case 'ship_dvd':
             case 'ship_dvd_only':
                 $numDisks = $itemCount['DVD']['count'];
                 break;
             case 'ship_cd':
                 $numDisks = $itemCount['CD']['count'];
                 break;
         }
         $shippingCharge = OrdersController::calculateShippingFee($numDisks);
     }
     return $shippingCharge;
 }