how can I call method class list

[abab]

If I have class with static field:

public class Cart
{
        private static int quantity_all_books = 0; 

        public int id { get; private set; }
        public int quantity { get; private set; }

        public Cart(int x, int y)
        {
            quantity_all_books++;

            id = x;
            quantity = y;
        }
}

And I have list type of this class:

List<Cart> shopping = new List<Cart>();
shopping.Add(new Cart(53, 2));
shopping.Add(new Cart(44, 1));

How can I check value static field quantity_all_books. I have tried make this field public, write method which return value of this field. But when I write "shopping." Visual Studio don't give me on the list this field or method.