Hi,
Please refer below code.
C#
List<Users> users = new List<Users>();
users.Add(new Users
{
    Id = 1,
    Type = "admin"
});
users.Add(new Users
{
    Id = 2,
    Type = "customer"
});
List<Transactions> transactions = new List<Transactions>();
transactions.Add(new Transactions
{
    Id = 1,
    UserId = 1,
    Amount = 200
});
transactions.Add(new Transactions
{
    Id = 2,
    UserId = 2,
    Amount = 200
});
transactions.Add(new Transactions
{
    Id = 3,
    UserId = 1,
    Amount = 200
});
List<Transactions> customerTransactions = (from transaction in transactions
                                            join user in users on transaction.UserId equals user.Id
                                            where user.Id == 1
                                            select transaction).ToList<Transactions>();
Transactions and Users Class
public class Transactions
{
    public int Id { get; set; }
    public int UserId { get; set; }
    public int Amount { get; set; }
}
public class Users
{
    public int Id { get; set; }
    public string Type { get; set; }
}
I hope this will help you out.