$matieres = array("Français", "Mathématiques", "Physique");
$notes = array( 12, 14, 16);
$coefficients = array(2, 6, 4);

$somme_notes = 0;
$somme_coefs = 0;
for ($i = 0; $i < count($notes); ++$i) {
    echo "<tr><td>". $matieres[$i] ."</td>";
    echo "<td class=\"right\">". $notes[$i] ."</td>";
    echo "<td class=\"right\">". $coefficients[$i] ."</td></tr>";
    $somme_notes += $notes[$i] * $coefficients[$i];
    $somme_coefs += $coefficients[$i];
}
$moyenne = $somme_notes / $somme_coefs;
$moyenne = round($moyenne * 100) / 100.0;
echo "<tr><td>Total :</td><td  colspan=\"2\" class=\"right\"> $moyenne </td></tr>";