public ActionResult ChangeReturnForm(ChangeReturnValidation model)
        {
            if (ModelState.IsValid)
            {
                var calc = new ReturnChangeOperations();
                var request = new ReturnChangeRequest();

                request.Cost = model.Cost.Value;
                request.EnteredCash = model.EnteredCash.Value;
                request.Product = model.Product;

                var response = calc.CalculateDifferent(request);

                var result = calc.CalculateChange(response);

                return View("ChangeReturnResult", result);
            }
            return View(model);
        }
 public ReturnChangeResponse CalculateDifferent(ReturnChangeRequest request)
 {
     response.DifferenceChange = decimal.Subtract(request.EnteredCash, request.Cost);
     return response;
 }