Как сделать так, чтобы програма понимала какое число больше

Надо чтобы эта програма выводила лучших учеников по среднему балу.

Вот код:

<?
    $inform=array(
        1=>array("Василь",12,"н",8,"н","н",10,10),
        2=>array("Маша",8,"","н","",4,"н",7),
        3=>array("Ирина","н",11,"","н",7,"",6),
        4=>array("Никита","",8,8,9,"","н",7),
        5=>array("Саша","н","н","н","",9,"н",7),
        6=>array("Коля",9,"",8,10,10,11,12),
        7=>array("Гриша",9,"","","","",7,"н"),
        8=>array("Оля","н","н","","",6,"",""),
        9=>array("Галя",4,5,"","н","н","н",5),
        10=>array("Тарас",10,10,8,"н",11,12,9));
    echo "<table border='1' width='400'>";
       echo "<tr>";
            echo "<th>Номер</th>";
            echo "<th>Им'я ученика</th>";
            echo "<th>1</th>";
            echo "<th>2</th>";
            echo "<th>3</th>";
            echo "<th>4</th>";
            echo "<th>5</th>";
            echo "<th>6</th>";
            echo "<th>7</th>";
            echo "<th>Сер.<br>бал</th>";
        echo "</tr>";   
        foreach ($inform as $key=>$st){
        echo "<tr>";
            echo "<td>".$key."</td>";
               $n=0;
               $sum=0;
                foreach ($st as $value){
                    echo "<td>".$value."</td>";
                    if($value>0) {
                    $sum=$sum+$value;
                        $n++;
                    }   
                }   
                $ser=$sum/$n;
                echo "<td>".round($ser,2)."</td>";
            echo "</tr>";
        }   
    echo"</table>"; 

?>