How can i group by Month and sum same month branches In Linq C# [Resolved]

(from item in listDetails

                    group item by new{item.Branch.BranchId,item.Month.MonthId} into grouping

                    select new ListDetailsBE()

                    {

                        ListId =grouping.FirstOrDefault().ListId,

                        Month = grouping.FirstOrDefault().Month.MonthName,

                        MonthId = grouping.Key.MonthId,

                        Amount = grouping.Sum(x=>x.Amount),

                        BranchId = grouping.Key.BranchId,

                        BranchName = grouping.FirstOrDefault().Branch.BranchName

                    }).ToList();