Hello, I have Odoo 8 and I am developing a QWeb report. Is there any way to sum any field in a t-foreach loop and then display the result of the sum? How?

Thanks!       

EDIT

...            
       <t t-set="total" t-value="0" />

            <table class="table table-condensed">
                <thead>
                    <tr>
                        <th>Fecha</th>
                        <th>Documento</th>
                        <th>Detalle</th>
                        <th>Total sin impuestos</th>
                        <th>Total con impuestos</th>
                    </tr>
               </thead>
               <tbody class="sale_tbody">

                    <tr t-foreach="docs" t-as="l">
                        <td>
                           <span t-field="l.date_order"/>
                        </td>
                        <td>
                            <span t-field="l.name"/>
                        </td>
                        <td>
                            <table class="table table-condensed">
                                <thead>
                                    <tr>
                                        <th>Producto</th>
                                        <th>Cantidad</th>
                                        <th>Precio unitario</th>
                                        <th>Fecha del viaje</th>
                                        <th>Destino</th>
                                        <th>Remito SyE</th>
                                        <th>Chofer</th>
                                        <th>Subtotal</th>
                                    </tr>
                                </thead>
                                <tbody>
                                    <tr t-foreach="l.order_line" t-as="a">
                                        <td>
                                            <span t-field="a.product_id" />
                                        </td>
                                        <td>
                                            <span t-field="a.product_uom_qty" />
                                        </td>
                                        <td>
                                            <span t-field="a.price_unit" />
                                        </td>
                                        <td>
                                            <span t-field="a.fecha" />
                                        </td>
                                        <td>
                                            <span t-field="a.destino" />
                                        </td>
                                        <td>
                                            <span t-field="a.numero_remito" />
                                        </td>
                                        <td>
                                            <span t-field="a.chofer" />
                                        </td>
                                        <td>
                                            <span t-field="a.price_subtotal" />
                                        </td>
                                    </tr>   
                                </tbody>
                            </table>
                        </td>
                        <tr>
                            <td /><td /><td />
                            <td>
                                <span t-field="l.amount_untaxed" />
                            </td>
                            <td>
                                <span t-field="l.amount_total" />
                            </td>

                            <t t-set="total" t-value="total+l.amount_total" />

                        </tr>
                    </tr>                    
                </tbody>
            </table>

            <h3>Total: $<t t-esc="total" /></h3>             

In bold I mark the lines where I do the sum.