After clicking button, dropdown list selected index is going back to '0' in MVC3

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ASP.NET

MVC3

Hi all,
After clicking button, dropdown list selected index is going back to '0'. How to maintain to not go to zero in MVC3.
My code is
View is:

@using (Html.BeginForm())
{
    @Html.ValidationSummary(true)
    <div>
        <div style="float: left">
            States Filter :</div>
        <div style="float: left; padding-removed 20px">@Html.DropDownList("Areas", ViewData["Areas"] as SelectList, "-select state-", new {@style = "width:200px;" })</div>
    </div>
    <div style=" padding-removed30px">
        
            <input type="image" value="submit" src="../../Images/FilterBrowse.gif" alt="submit Button"  />
        
    </div>
    
}
for each loop table(Gridview)

Controller is:

//[Authorize]
        public ActionResult States()//int? id)
        {
            ViewData["Areas"] = new SelectList(am.FindUpcomingStates222().ToList(), "state_Name", "state_Name");
            var state = am.FindUpcomingStates().ToList();
            if (state != null)
            {
                ViewData["name"] = true;
                return View("States", state);
            }
            else
                return View("NotFound");
        }


[AcceptVerbs(HttpVerbs.Post)]
        public ActionResult States(string _stateName, FormCollection formvalues)
        {
            _stateName = Request.Form["Areas"].ToString();
            ViewData["Areas"] = new SelectList(am.FindUpcomingStates222().ToList(), "state_Name", "state_Name", _stateName);
            if (_stateName == "")
            {                
                return View();
            }
            else
            {                
                var state = am.FindUpcomingStates22(_stateName).ToList();
                if (state != null)
                    return View("States", state);
                else
                    return View("NotFound");
            }
        }

Thanks,
Sampath bejugama