namespace PL

{

    public class PresentationObject

    {

        private BLL.BusinessObject bobj = new BLL.BusinessObject();

        protected void ddl_Customers_SelectedIndexChanged(object sender, System.EventArgs e)

        {

            string selectedValue = "Some String";

            var result = bobj.returnTicket(selectedValue);

        }

    }

}

​

namespace BLL

{

    public class BusinessObject

    {

        public string returnTicket(DLL.collection b)

        {

            return string.Empty;

        }

    }

}

​

namespace DLL

{

    public class collection

    {

        public string SupportRef1 { get; set; }

    }

}

​

public class Program

{

    public void Main()

    {

    }

}