How to filter index action by passing multiply parameters

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.NET

MVC5

Can you please anyone help me how to filter index by passing multiple parameters.
My model is
City which have CountryId and StateId So the user first select country and then state
and then enter name of city.
How can i do my code is given below.
Thank you

public ActionResult Index(string searchString, string currentFilter, int? page, string sortOrder)
      {
          ViewBag.CurrentSort = sortOrder;
          ViewBag.NameSortParm = String.IsNullOrEmpty(sortOrder) ? "name_desc" : "";


          if (searchString != null)
          {
              page = 1;
          }
          else
          {
              searchString = currentFilter;
          }

          ViewBag.CurrentFilter = searchString;

          var result = from c in db.cities
                       select c;

          if (!String.IsNullOrEmpty(searchString))
          {

              result = result.Where(c => c.CityName.Contains(searchString));

          }
          result = result.OrderByDescending(x => x.CountryId);

          int pageSize = 6;
          int pageNumber = (page ?? 1);
          return View(result.ToPagedList(pageNumber, pageSize));
      }