function get_average_readers($feed_id,$interval = 7){ 
    $today = date('Y-m-d', strtotime("now")); 
    $ago = date('Y-m-d', strtotime("-".$interval." days")); 
    $feed_url="https://feedburner.google.com/api/awareness/1.0/GetFeedData?uri=".$feed_id."&dates=".$ago.",".$today; 
    $ch = curl_init(); 
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1); 
    curl_setopt($ch, CURLOPT_URL, $feed_url); 
    $data = curl_exec($ch); 
    curl_close($ch); 
    $xml = new SimpleXMLElement($data); 
    $fb = $xml->feed->entry['circulation']; 
 
    $nb = 0; 
    foreach($xml->feed->children() as $circ){ 
        $nb += $circ['circulation']; 
    } 
 
    return round($nb/$interval); 
}