Any ideas for a php code for this?

I need to make some math, and I cannot seem to find a way to do it.

I have the following table, resulting from this query:

SELECT materii.id,
       materii.materie,
        GROUP_CONCAT(note.note) AS note,
        GROUP_CONCAT(DISTINCT teza.`teza`) AS teza


FROM materii
LEFT JOIN teza ON materii.id = teza.id_materie
LEFT JOIN note ON materii.id = note.id_materie
LEFT JOIN elevi ON note.id_elev = elevi.cod_elev 
LEFT JOIN luni ON note.`luna_nota`=luni.`id`
WHERE elevi.`cod_elev` = 1 AND luna_nota = 9
GROUP BY materii.id, materii.materie
ORDER BY materii.materie

I need to do something like :

$notele = mysql_query($pentrumedie)
                or die("Nu am gasit note in baza de date");
$numar_note = mysql_num_rows($notele);
if($numar_note==0)
{

}
else 
{
    while($rand2=mysql_fetch_array($notele))
    {     
         $note1 = ($rand2['notele'] / $numar_note);
       $medie_septembrie = ($note1 / $cate_note_sunt);
    }
}

I need to do something like that for all the "note", but $rand2['notele'] needs to be the sum of them, if there are more "note", and if there is a value for "teza", then the math formula needs to be:

(($rand2['notele'] / $numar_note) * 3 + teza) / 4

I tried some if functions, but none of them work....Any Ideas? Thanks!!!