Get the sum of column using Entity Framework in ASP.Net

hello i'm trying to implement the following sql statement using entity framework 

select coalesce(SUM(cdin_ActMortgageAmnt),0) from CRM.dbo.CDIndex,CRM.dbo.company  where comp_companyid=cdin_companyid and comp_idcust like '%10319%' and cdin_Deleted is null and cdin_startunstufdate is not null and cdin_Status='InProgress'  

Company c = db.Companies.Find(750);  
      var CGP = (from cd in db.CDIndexes  
                 join com in db.Companies on cd.cdin_CompanyId equals com.Comp_CompanyId  
                 where  
                 com.Comp_IdCust == c.Comp_IdCust &&  
                 cd.cdin_Deleted == null &&  
                 cd.cdin_startunstufdate == null &&  
                 cd.cdin_Status == "InProgress"  
                 select new  
                 {  
                  act=cd.cdin_ActMortgageAmnt  
  
                 }  
               );  
      var query = CGP.Sum(x => x.act);  
      lblSum.Text = query.ToString();  

but when i trace the code var query gives me null ? Please help