如何实现 剩余工时自动计算已解决悬赏20积分

 public function recordEstimate($taskID)
{
$this->commonAction($taskID);

if(!empty($_POST))
{
$this->task->recordEstimate($taskID);
if(isonlybody()) die(js::closeModal('parent.parent', 'this'));
die(js::locate($this->createLink('task', 'view', "taskID=$taskID"), 'parent'));
}

$this->session->set('estimateList', $this->app->getURI(true));

$this->view->task = $this->task->getById($taskID);
$this->view->estimates = $this->task->getTaskEstimate($taskID);
$this->view->title = $this->lang->task->record;
$this->display();

}

就是我输入日期和工时 他会自动算出剩余工时 这个如何在代码中实现 该如何写