linq sum where

 IList<StuItem> stEntityList = new List<StuItem>();
            StuItem stBll = new StuItem();
            stEntityList = stBll.GetModelList("");
 
            int totalScore = (from s in stEntityList where s.SScore != null select s.SScore).Sum().Value;

 int totalScore = 0;
             foreach (StuItem sientity in stEntityList)
            {
                 if (sientity.SScore != null)
                {
                    totalScore += sientity.SScore.Value;
                }
                
             }