Výpočet DPH - Zobrazí se nula

    <?php do_action( 'woocommerce_cart_totals_before_order_total' ); ?>
     <?php 
    $cena = wc_cart_totals_order_total_html();
    $dan=($cena * ((21)/100));
 ?>     
        <tr class="order-total">
            <th><?php _e( 'Total', 'woocommerce' ); ?> </th>
            <td><?php wc_cart_totals_order_total_html(); ?>
     
      <?php echo $dan; ?></td>
        </tr>

function wc_cart_totals_order_total_html() {
    $value = '<strong>' . WC()->cart->get_total() . '</strong> ';