laravel 5.2 - Trying to get property of non-object, exactly i don't this error -

this controller questions , it's category, should displayed users category, category user select must displayed , count questions users answered ,but when want apply section mentioned error displaying don't error

contrller

 public function start()     {         $category = db::table('question_type')->get();         return view('frontend.start',compact('category'));     }     public function questionscategory(request $request)     {         $ctid = $request->input('selected-category');         $langid = $request->input('language');         $time = db::table('question_type')->select('time')->where('type_id', $ctid)->first();         $hours = 0;         $minutes = 0;         $scs = 0;         if ($ctid == 1)         {             if ($time->time > 60)             {                 $hours = 1;                 $minutes = $time->time- 60;             }             else {                 $hours = 0;                 $minutes = $time->time;             }         }         elseif ($ctid == 2)         {             if ($time->time > 60)             {                 $hours = 1;                 $minutes = $time->time- 60;             }             else {                 $hours = 0;                 $minutes = $time->time;             }         }         elseif ($ctid == 3)         {             if ($time->time > 60)             {                 $hours = 1;                 $minutes = $time->time- 60;             }             else {                 $hours = 0;                 $minutes = $time->time;             }         }         elseif($ctid == 4) {             if ($time->time > 60)             {                 $hours = 1;                 $minutes = $time->time- 60;             }             else {                 $hours = 0;                 $minutes = $time->time;             }         }          $category = db::table('question_type')->select('type_name')->where('type_id',$ctid)->first();         $questions = db::table('questions')->join('question_type','question_type.type_id','=','questions.type_id')             ->select('questions.*','question_type.*')             ->where('questions.lang_id',$langid)->where('questions.type_id',$ctid)->limit(43)->get();         $cat_done = db::table('student_answers')             ->select('student_answers.*')->first();         if ($cat_done->student_id == auth()->user()->id && $cat_done->question_id >=42)         {             dd("you have done category");         } //->inrandomorder()         return view('frontend.category-questions',compact('category','questions','hours','minutes','ctid','langid'));     }     public function categoryover()     {         return view('frontend.time-over')->render();     }     public function darianswers(request $request)     {         $catid = $request->input('category');         $lang = $request->input('language'); //dd($request->all());         $questions = db::table('questions')->join('question_type','question_type.type_id','=','questions.type_id')             ->select('questions.*','question_type.*')             ->where('questions.lang_id',$lang)             ->where('questions.type_id',$catid)->limit(43)->get();          ($i=1; $i<=count($questions); $i++)         {             $qid = $request->input('qid'.$i);             $answer = $request->input('answer'.$i);             $status = db::table('student_answers')->insert([                 'student_id' => auth()->user()->id,                 'question_id' => $qid,                 'st_answer' => $answer             ]);         }         if ($status != 0)         {             if ($catid == 4)             {                 return redirect('/student/choices');             }             else {                 return redirect('/start')->with('success','این بخش موفقانه تمام شد!');             }         }         else {             return back()->with('error','خطا رخ داده، دوباره سعی نمایید.');         }     }     public function studentchoices()     {         $provinces = db::table('provinces')->select('*')->get();         $unvs = db::table('university')->select('*')->get();         $faculty = db::table('faculty')->select('*')->get();         $depart = db::table('department')->select('*')->get();         return view('student.choices',compact('provinces','unvs','faculty','depart'));     } }                      routes: oute::get('/', 'pagescontroller@index');`enter code here` route::get('start','pagescontroller@start');`enter code here`   //end of student routes  // user routes   route::get('student/register', 'studentcontroller@getregister');  route::post('student/store', 'studentcontroller@postregister');    route::post('filter/districts','studentcontroller@filterdistricts');   //end of user route       route::post('question/category','studentcontroller@questionscategory');     route::get('question/category','studentcontroller@categoryover');     route::post('question/answer','studentcontroller@darianswers');       route::get('student/choices','studentcontroller@studentchoices');