LatestState

var customers = 
	new List<Customer>
	{
		new Customer { Id = 1, Name = "ABC" },
		new Customer { Id = 2, Name = "DEF" }
	};

var transactions = 
	new List<TransactionFlow>
	{
		new TransactionFlow { Id = 1, Date = new DateTime(2000,1,1), TransactionId = 1, Status = "Submit" },
		new TransactionFlow { Id = 2, Date = new DateTime(2000,1,1), TransactionId = 2, Status = "Submit" },
		new TransactionFlow { Id = 3, Date = new DateTime(2000,2,1), TransactionId = 1, Status = "Process" },
		new TransactionFlow { Id = 4, Date = new DateTime(2000,2,1), TransactionId = 2, Status = "Process" },
		new TransactionFlow { Id = 5, Date = new DateTime(2000,3,1), TransactionId = 2, Status = "Finish" }
	};

var states = 
	new List<TranscationState>
	{
		new TranscationState { Level = 1, State = "Submit" },
		new TranscationState { Level = 3, State = "Process" },
		new TranscationState { Level = 9, State = "Finish" }
	};

var results = 
	transactions
		.Select(s => new
			{
				s.TransactionId,
				s.Status,
				StateLevel = states.First(p => p.State.Equals(s.Status)).Level
			})
		.GroupBy(ks => 
			 ks.TransactionId, 
			 (k, g) => new
			 {
				 Id = k, 
				 Items = g
			 })
		.Select(g =>
			{
				var i = g.Items.First(p => p.StateLevel.Equals(g.Items.Max(s => s.StateLevel)));
				return new
				{
					Id = i.TransactionId, 
					CustomerName = customers.First(p => p.Id.Equals(i.TransactionId)).Name, 
					i.Status
				};
			})
		.ToList();