How to sum a colum using LINQ

Hi

i have a table reservationbydate i n that i have hotelid,type of room,date and noofroom.I should get the total no of rooms for aparticular date.How to do that.

 DateTime StartDate = Convert.ToDateTime(Txt_Checkindate.Text);
        DateTime EndDate = Convert.ToDateTime(Txt_Checkoutdate.Text);

        var avaliabiltyQuery = from a in db.tbl_ReservationByDates
                               where a.HotelID == HotelId
                               && a.RoomType == Drp_TypeOfRoom.Text
                               && a.BookedDate == StartDate

                               select new {how to get the sum of noofroom column
                               
                               };