How to Use Join Condition in LINQ Query in C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

/// <summary>
/// Summary description for Join
/// </summary>

public class Join
{
    public Join()
    {

    }
    public void JoinLinq()
    {
        List<Student> student = new List<Student>();
        List<StudentInfo> studentInfo = new List<StudentInfo>();

        var cust = (from a in student
                    join b in studentInfo on a.RollNo equals b.RollNo
                    select a).ToList();
    }
}
public class Student
{
    public string Name;
    public string RollNo;
    public string FatherName;
}
public class StudentInfo
{
    public string BookNo;
    public string RollNo;
    public string BookID;
}