use array with where in laravel

$assignquestion = DB::table('assign_question')->where('user_id',$user_id)->get();
    $assignq = array();
    foreach($assignquestion as $assign)
    {
    $assignq = array_merge($assignq,json_decode($assign->question_ids,true));
    }
    $data = DB::table('question_master')->whereIn('id',$assignq)->paginate(50);