How to sum an item present in a pivot table with laravel?

Question

I have 3 tables: products, orders and pivot table (order_product).

And these models:

class Product extends Model
{
    public function orders()
    {
        return $this->belongsToMany(Order::class)
            ->withPivot([
                'quantity',
            ]);
    }
}

class Order extends Model
{
    public function products()
    {
        return $this->belongsToMany(Product::class)
            ->withPivot([
                'quantity',
            ]);
    }
}

I'd like to do a query where for each product have ordered quantity.

Thanks