Linq Query in asp.net mvc

Question

public ActionResult CommulativeCAmount()

{

MPOWERINGDBContext db = new MPOWERINGDBContext();

DateTime twelveMonthsBeforeNow = DateTime.Now.AddMonths(-12);

var comid = Convert.ToInt32(Session["MyId"]);

var query = db.Cases.Where(x => x.CompanyID == comid).Where(x => x.ReceievedDate >= twelveMonthsBeforeNow)

.GroupBy(p => new { p.ReceievedDate.Value.Month,p.ReceievedDate.Value.Year })

.OrderBy(x=>x.Key.Year)

.Select(g => new {

mymonth = (string)g.Key.Month.ToString(),

myAmount = (double)g.Sum(w => w.TotalCollection),

}).ToList();

return Json(query, JsonRequestBehavior.AllowGet);

}

 

i want to store commulative sumamount  in myAmount  using linq query above is my linq query data show correct but i want to show commulative amount?