get data of last month in laravel code example

Example: laravel eloquent get 3 months

$dateS = Carbon::now()->startOfMonth()->subMonth(3);
$dateE = Carbon::now()->startOfMonth(); 
$TotalSpent = DB::table('orders')
->select('total_cost','placed_at')
->whereBetween('placed_at',[$dateS,$dateE])
->where(['deleted' => '0', 'delivery_address_id' => $DeliveryAddress->id])
->sum('total_cost');