ticket space by 10

function my_mod_ticketlist($ob, $zero_value, $default_value, $EM_Ticket){
 $available_spaces = $EM_Ticket->get_available_spaces();
 if( $EM_Ticket->is_available() ) {
  $min_spaces = $EM_Ticket->get_spaces_minimum();
  $default_value = $min_spaces > $default_value ? $min_spaces:$default_value;
  $default_value = $default_value * 10;
  ?>
  <select name="em_tickets[<?php echo $EM_Ticket->ticket_id ?>][spaces]" class="em-ticket-select" id="em-ticket-spaces-<?php echo $EM_Ticket->ticket_id ?>">
   <?php
    $min = ($EM_Ticket->ticket_min > 0) ? $EM_Ticket->ticket_min:1;
    $max = ($EM_Ticket->ticket_max > 0) ? $EM_Ticket->ticket_max:get_option('dbem_bookings_form_max');

   ?>
   <?php if($zero_value && $min_spaces == 0) : ?><option>0</option><?php endif; ?>
   <?php for( $i=$min; $i<=$available_spaces && $i<=$max; $i++ ): ?>
   <?php $new_value = $i * 10; ?>
   <option <?php if($new_value == $default_value){ echo 'selected="selected"'; $shown_default = true; } ?>><?php echo $new_value ?></option>
   <?php endfor; ?>
   <?php if(empty($shown_default) && $default_value > 0 ): ?><option selected="selected"><?php echo $new_value; ?></option><?php endif; ?>
  </select>
  <?php
 }
 return ob_get_clean();
}
add_filter('em_ticket_get_spaces_options','my_mod_ticketlist',10,4);