How to Select the Highest value in each Group in linq?

public class CUSTOM_STU_DETAIL

{

public string Re_Admission_Type { get; set; }

public DateTime? Re_Admission_Date { get; set; }

public long? Registration_Id { get; set; }

public string Admission_No { get; set; }

public long? Class_Id { get; set; }

public long? Section_Id { get; set; }

public long? Academic_Year_Id { get; set; }

public string Student_First_Name { get; set; }

public string Student_Last_Name { get; set; }

public DateTime? Date_Of_Birth { get; set; }

public string Gender { get; set; }

public string Blood_Group { get; set; }

public long? Cast_Id { get; set; }

public long? Religion_Id { get; set; }

public long? Roll_Id { get; set; }

public string Set_New_RollNo { get; set; }

public long? Company_ID { get; set; }

public long? COMPANY_LOCATION_ID { get; set; }

public string STUDENT_NAME { get; set; }

//public DateTime Attendance_Date { get; set; }

public string Academic_Year_Name { get; set; }

public string Class_Name { get; set; }

public string Section_Name { get; set; }

}

List academicYr = new List();

if (CompanyId != null && CompanyId != 0 && CompanyLocationId != null && CompanyLocationId != 0 && ClassID != null && ClassID != 0 && SectionID != null && SectionID != 0)

{

academicYr = (from s in db.Student_Re_Admission

group s by s.Registration_Id into stugrp

let topp = stugrp.Max(x => x.Re_Admission_Id)

select new CUSTOM_STU_DETAIL

{

Re_Admission_Type = topp.Re_Admission_Type,

Re_Admission_Date = b.Re_Admission_Date,

Registration_Id = b.Registration_Id,

Admission_No = b.Admission_No,

Class_Id = ClassID,

Section_Id = SectionID,

Academic_Year_Id = b.Academic_Year_Id,

Student_First_Name = b.Student_First_Name,

Student_Last_Name = b.Student_Last_Name,

Date_Of_Birth = b.Date_Of_Birth,

Gender = b.Gender,

Blood_Group = b.Blood_Group,

Cast_Id = b.Cast_Id,

Religion_Id = b.Religion_Id,

Roll_Id = a.Roll_Id,

Set_New_RollNo = a.Set_New_RollNo,

Company_ID = CompanyId,

COMPANY_LOCATION_ID = CompanyLocationId,

STUDENT_NAME = a.Student_First_Name + " " + " " + a.Student_Last_Name,

}).ToList();