Calculation of time arrays by $_POST in PHP

Question

I have a dynamic form from which comes the name of the interruption, start time and end time. It must return the interruptions and times added, but in the total field of lost hours it has to subtract the ending by the beginning and add another interruption if it has. Example below:

The problem is that it’s showing in total, the first calculation, and the sum. Code below:

  $mostrar = 0;
  $somah = 0;
  $somam = 0;
  for ($i=0; $i < count($_POST['interrupcao']); $i++) {

   $total = strtotime($_POST['terminoint'][$i]) - strtotime($_POST['inicioint'][$i]);
   $horas      = floor($total / 60 / 60);
   $minutos    = round(($total - ($horas * 60 * 60)) / 60);

   $somah += $horas;
   $somam += $minutos;

   $mostrar .= $somah.":".$somam;

   $html .="<tr>";
   $html .="<td>{$_POST['interrupcao'][$i]}</td>";
   $html .="<td>{$_POST['inicioint'][$i]}</td>";
   $html .="<td>{$_POST['terminoint'][$i]}</td>";
   $html .= "</tr>";
  }