public function learnerQuizMember($chapter_id, $user = null)
 {
     if ($user) {
         $this->setUser($user);
     }
     $chapter = Chapter::find($chapter_id);
     $quiz = $chapter->quiz;
     $member = null;
     foreach ($quiz->members as $data) {
         if ($data->user_id == $this->user->id) {
             $member = $data;
             break;
         }
     }
     return $member;
 }