File upload error

Hi guys here is my controller

 // Handle File Upload
        if($request->hasFile('file_url')){
            // Get filename with the extension
            $filenameWithExt = $request->file('file_url')->getClientOriginalName();
            // Get just filename
            $filename = pathinfo($filenameWithExt, PATHINFO_FILENAME);
            // Get just ext
            $extension = $request->file('file_url')->getClientOriginalExtension();
            // Filename to store
            $fileNameToStore= $filename.'_'.time().'.'.$extension;
            // Upload Image
            $path = $request->file('file_url')->storeAs('public/assignments', $fileNameToStore);
        }         
    // Create Book
        $book = new Library;
        $book->title = $request->input('title');
        $book->author = $request->input('author');
        $book->type = $request->input('type');
        $book->availability = $request->input('availability');
        $book->file_url = $fileNameToStore;
        $book->save();
        return redirect('/library')->with('success', 'Book Created');

Here is my form:-

@extends('layouts.app')
@if(Auth::user()->isAdmin() || Auth::user()->isLibrarian())
@section('content')
    <h3 class="page-title">Add Book</h3>
    {!! Form::open(['method' => 'POST','enctype'=> 'multipart/data', 'route' => ['library.store']]) !!}

    <div class="panel panel-default">
        <div class="panel-heading">
            @lang('quickadmin.create')
        </div>

        <div class="panel-body">
            <div class="row">
                <div class="col-xs-12 form-group">
                    {!! Form::label('title', 'Title*', ['class' => 'control-label']) !!}
                    {!! Form::text('title', old('title'), ['class' => 'form-control','placeholder' => 'Title']) !!}

                </div>
            </div>

            <div class="row">
                <div class="col-md-12 form-group">
                    {!! Form::label('author', 'Author *', ['class' => 'col-sm-2 control-label']) !!}
                    {!! Form::text('author', old('author'), ['class' => 'col-sm-10 form-control ', 'placeholder' => 'Author']) !!}

                </div>
            </div>
            <div class="row">
                <div class="col-md-12 form-group">
                    {!! Form::label('type', 'Type *:', ['class' => 'col-sm-2 control-label']) !!}
                    {!! Form::select('type', array('E-book' => 'E-book', 'Hardcover' => 'Hardcover'), ['class' => 'col-sm-10 form-control']) !!}
                </div>
            </div>
            <div class="row">
                <div class="col-xs-12 form-group">
                    {!! Form::label('availability', 'Availability *', ['class' => 'col-sm-2 control-label']) !!}
                    {!! Form::select('availability', array('Available' => 'Available', 'Unavailable' => 'Unavailable'), ['class' => 'col-sm-10 form-control']) !!}
                </div>
            </div>
            <div class="row">
                <div class="col-xs-12 form-group">
                    {!! Form::label('Upload E-Book', 'E-book Upload *', ['class' => 'col-sm-2 control-label']) !!}
                    {!! Form::file('file_url') !!}
                </div>
            </div>
        </div>
    </div>

    {!! Form::submit(trans('quickadmin.save'), ['class' => 'btn btn-success']) !!}
    {!! Form::close() !!}
@endif
@stop

The issue is that when I click on submit to save it to DB it says variable fileNameToStore not found

I have created the linking between the folder storage and public