LINQ Query with group,join and sum

var gname = from S in qryGen.T_Grn_details
join G in qryGen.T_Grade_Masters on S.F_GradeMaster_Id equals G.F_GradeMaster_Id
where S.F_Grn_Id == int.Parse(cboGRNNumber.SelectedValue.ToString())
group S by new {G.F_GradeName_Id,G.F_GradeName} into d
select new {d.Key.F_GradeName_Id,
d.Key.F_GradeName,
TotalWeight = d.Sum(o => o.F_Weight)};