public string Save(Enroll aEnroll)
        {
            if (aEnrollGateway.IsExist(aEnroll))
            {
                return("This Course Already Enrolled");
            }

            if (aEnrollGateway.Save(aEnroll) > 0)
            {
                return("Enrollment Successfully Done");
            }
            else
            {
                return("Failed");
            }
        }