How to calculate two data in differents table with laravel 8? [closed]

I have made a form to order some products. In that form, I want to decrease Saldo data from the users table and item_price from the items table. But I didn't know to decrease the two data. I have made it like this. Please help me.

<div class="container">
    <div class="row">
        <div class="col-md-12">
            <div class="card">
                <div class="card-header">
                    <h3>Order</h3>
                    @if (session('status'))
                        <div class="alert alert-success" role="alert">
                            
                        </div>
                    @endif
                </div>
                <div class="card-body">
                    <div class="row">
                        <div class="col-md-6">
                            <form action="/orderitems" method="POST">
                                
                                
                                <div class="form-group">
                                    <label for="order_item">Order Item</label>
                                    <select name="order_item" class="form-control">
                                        @foreach ($items as $item)
                                            <option value=""></option>
                                        @endforeach
                                    </select>
                                </div>
                                <input type="hidden" name="email_order" value="">
                                <input type="hidden" name="order_time" value="">
                                <input type="hidden" name="saldo" value="">
                                <input type="hidden" name="order_desc" value="belum selesai">
                                <div class="form-group">
                                    <label for="game_id">ID GAME</label>
                                    <input type="text" name="game_id" class="form-control" >
                                </div>
                                
                                <button type="submit" class="btn btn-success">Pesan</button>
                                <a href="/home" class="btn btn-danger">Batal</a>
                            </form>
                        </div>
                    </div>
                </div>
            </div>
        </div>
    </div>
</div>

Here is the controller:

    public function orderitems(Request $request)
{
    $orders = new Orders();

    $orders->order_time= $request->Input('order_time');
    $orders->email_order = $request->Input('email_order');
    $orders->order_item = $request->input('order_item');
    $orders->game_id = $request->Input('game_id');
    $orders->order_desc = $request->Input('order_desc');

    $email = $request->Input('email_order');
    $itemcode = $request->input('order_item');
    $saldo = DB::table('users')->where('email', $email)->pluck('saldo');
    $harga = DB::table('items')->where('code_item', $itemcode)->pluck('item_price');

    
    if($saldo >= $harga){
        $updateSaldo = User::find($email);
        $sisaSaldo = $saldo - $harga;
        $updateSaldo->saldo = $sisaSaldo;
        $updateSaldo->update();
        $orders->save();
        return redirect('/order')->with('status', 'Pesanan Anda Berhasil Terkirim dan Saldo anda telah dikurangi.');
    }else{
        return redirect('/order')->with('status', 'Saldo Anda tidak mencukupi silahkan tambah saldo.');
    }
  
}

I want to store the result of that two data to update the Saldo data in users table.