如何添加或乘以复选框的值

I am trying to sum up the values of checkbox value using a foreach loop... but i am confused as to where to add the signs so the values can add up.

Where do i include the addition sign so it can sum up whatever number value so i can get the total?

<?php 
if(isset($_POST["submit"])){
    $main_odds      = $_POST["total_odds"];
    if(!empty($main_odds)){
        echo "You have selected the following games ";
        foreach ($main_odds as $final_odd){
            echo "<td>$final_odd</td>" ;
        }
    }else{
        echo "You have not selected any odds";
    }

}
$total_odds = "";
?>

<table>
    <thead>
        <tr>
        <th>calculate</th>
        <th>odds</th>
        </tr>
    </thead>
    <tbody>
<?php foreach($games as $game): ?>
      <tr> 
       <td><?= $game->odds; ?></td>
        <td>
        <form method="Post" action="">
        <input type="checkbox" name="total_odds[]"  value="<?= $game->odds; ?>">
        </td>
      </tr>
         <?php endforeach; ?>
         <input type="submit" name="submit"/>
        </form>
         </tbody>
</table>

Add all values within the loop.

echo "You have selected the following games: ";
$total = 0;
foreach ($main_odds as $final_odd){
    $total += $final_odd;
    echo "<td>$final_odd</td>" ;
}
echo "<br>Total value is " . $total;

<?php 
$main_oddddd = "";
if(isset($_POST["submit"])){
     $main_odds      = $_POST["total_odds"];

    if(!empty($main_odds)){
        $val = 0;
        echo "You have selected the following games ";
        foreach ($main_odds as $final_odd){
             $val += $final_odd;
        }
    }else{
        echo "You have not selected any odds";
    }
    $main_oddddd = count($main_odds);
    echo $val;
}

?>

<?php 
$main_oddddd = "";
if(isset($_POST["submit"])){
     $main_odds      = $_POST["total_odds"];
    //echo $main_value     = implode(", ",  $main_odds);
    $total = 0;
    if(!empty($main_odds)){

        echo "You have selected the following games ";
        foreach ($main_odds as $final_odd){
            $total = $total * $final_odd;
        }
    }else{
        echo "You have not selected any odds";
    }
    $main_oddddd = count($main_odds);
    echo $total;
}

?>