Return value from function to ActionMethod in controller

Question

[HttpPost]
        public ActionResult AddVolunteer(VolunteerInfo viewModel)
        {
            if (!ModelState.IsValid)
            {
                return View("AddVolunteer", viewModel);
            }

            var volunteer = new VolunteerInfo()
            {
                Name = viewModel.Name,
                DonationForWhom = DonationValue() //Here's the error. Expecting a parameter

            };


            _context.VolunteerInfos.Add(volunteer);
            _context.SaveChanges();
            return RedirectToAction("Index", "Home");

        }



        public string DonationValue(string name)
        {
            return name; //not sure how to pass this above
        }

The error is in the 12th line: There is no argument given that corresponds to the required formal parameter 'name' of 'VolunteerInfoController.DonationValue(string)' VMS.

 

I don't know how to correct this. Please help me