FirsDemo.cs

private static void FirsDemo(List<Order> orders)
{
    var firstOrderAfterMarch = orders.First(order => order.OrderDate >= march);
    PrintHeaderFooter("First order after March", () => PrintOrder(firstOrderAfterMarch, indentBy), indentBy);

    var firstOrderAfterSeptember = orders.FirstOrDefault(order => order.OrderDate >= september);
    PrintHeaderFooter("First or Default order after September", () => PrintOrder(firstOrderAfterSeptember, indentBy), indentBy);
}