Calcul ligne par ligne dans un tableau PHP - MySQL

Bonjour,

J'ai un problème de calcul quand je veut afficher un total ligne par ligne dans un tableau, j'ai un champs "price" que je multiplie par la quantité "quantity" ça fonctionne sauf que dès que j'ai plus d'une ligne avec plus de 1 quantité le résultat est faux, j'arrive pas a m'en sortir voici mon code pour afficher :

require_once('../inc/connexion.php');
  $db = getDB();


  try {
} catch (PDOException $e) {
    die('Erreur : ' . $e->getMessage());
}
$stmt = $db->query("
SELECT a.nfacture, a.prixtotal, a.quantity, a.promo, a.customers, a.start_date, a.summary, a.state, a.numero, b.paid 
FROM
    (SELECT invoices.invoice as nfacture, SUM(services.price) as prixtotal, quantity as quantity, promotions.amount as promo, customers.fullname as customers, 	
    DATE_FORMAT(start_date,'%d/%m/%Y')  as start_date, states.state as state, invoices.numero as numero, comments.summary as summary 
    FROM invoices  
    LEFT JOIN customers ON (invoices.id_customers=customers.id_customers) 
    LEFT JOIN services ON (invoices.invoice=services.invoice)
    LEFT JOIN promotions ON (invoices.invoice=promotions.invoice)  
    LEFT JOIN items ON (services.id_items=items.id_items) 
    LEFT JOIN states ON (invoices.invoice=states.invoice) 
    LEFT JOIN comments ON (invoices.invoice=comments.invoice) 

    WHERE states.type = 1 AND (states.state = 1 OR states.state = 9) 
    GROUP BY nfacture 
    ) as a,
    (SELECT invoices.invoice as nfacture, SUM(payments.amount) as paid 
    FROM invoices
    LEFT JOIN payments ON (invoices.invoice=payments.invoice) 
    GROUP BY nfacture 
    ) as b 
WHERE a.nfacture=b.nfacture
ORDER BY nfacture DESC

");

  echo '

  <div class="card">
  <div class="card-header">
  <h3 class="card-title">Factures</h3>
  </div>
  <!-- /.card-header -->
  <div class="card-body">
  <table id="example1" class="table table-hover table-striped table-responsive">
  <thead>
  <tr>
  <th>ID</th>
  <th >Numéro</th>
  <th>Client</th>
  <th>Titre</th>
  <th>Price</th>
  <th>Paid</th>
  <th>Balance</th>
  <th>Date</th>
  <th>Statut</th>
  </tr>
  </thead>
  <tbody>
  ';


  while ($donnees = $stmt->fetch()) // Renvoit les valeurs de la bdd
  {
   
    $quantity = $donnees['quantity'];
    $promo = $donnees['promo'];
    $paid = $donnees['paid'];
    $prix = $donnees['prixtotal'] * $donnees['quantity'] ;

    echo $prix;



    // echo $tax['vat']; echo '<br>';
    // echo $donnees['prixtotal'];  echo '<br>';
    // echo $donnees['quantity'];  echo '<br>';  
    // echo $donnees['promo'];  echo '<br>';

    $total = $prix - $promo;

   // $balance = $total  - $paid;
   // $total = $prixtotal - $promo - $paid ;         
   // $balance = $total  - $promo  - $paid;

    $state = ($donnees['state']);


    if ($donnees['state'] == 1) {
      $state = '<span class="badge bg-warning" >En cours</span>';
    } elseif ($donnees['state'] == 2) {
      $state = '<span class="badge bg-success" >Payé</span>';
    } elseif ($donnees['state'] == 9) {
      $state = '<span class="badge bg-danger" >Annulée</span>';
    }

    echo '<tr>
    <td align="center" width="5%" ><a href="' . URLSITE . 'form/invoice.php?invoice=' . $donnees['nfacture'] . ' "><button type="button" class="btn btn-block btn-secondary btn-xs btn-flat">' . $donnees['nfacture'] . '</td></button></a>
    <td align="left" width="6%">' . $donnees['numero'] . '</td>
    <td align="left" width="30%">' . $donnees['customers'] . '</td>
    <td align="left" width="30%">' . $donnees['summary'] . '</td>';
    echo '<td align="left" width="5%">' . number_format($total, 2) . '  </td>';
    echo '<td align="left" width="5%"></></td>';
    echo '<td align="left" width="5%"></td>';
    echo '<td align="left" width="5%"> ' . $donnees['start_date'] . '  </td>';
    echo '<td align="left" width="5%">  ' . $state . ' </td>';
  }
  echo '
                </tbody>';
  echo '</tr>
                </tbody>
                <tfoot>
                <tr>
                <th>ID</th>
                <th >Numéro</th>
                <th>Client</th>
                <th>Titre</th>
                <th>Price</th>
                <th>Paid</th>
                <th>Balance</th>
                <th>Date</th>
                <th>Statut</th>
                </tr>
                </tfoot>
                </table>
                </div>
                <!-- /.card-body -->
                </div>
                <!-- /.card -->
                </div>
                <!-- /.col -->
                </div>
                <!-- /.row -->
                </div>';

  echo '            
                
                
                </table>
                </div>
                <!-- /.card-body -->
                </div>
                <!-- /.card -->
                </div>
                <!-- /.col -->
                </div>
                <!-- /.container-fluid -->
                ';

  ?>

si quelqu'un pouvait m'aider à trouver la solution.

Merci