sql trigger to update another table and get old value too

I have two table data and data1

data has two coloumns student id and marks

i need to create trigger which will update marks from data and will display marks into data1 with 4 coloumns

studntid, new_marks,old_marks,date

i have written a code but it is not showing old marks it just updates new marks and rest fileds.

CREATE TRIGGER marksss
       ON [dbo].[data] after UPDATE
AS
declare @studentid int;
declare @marks int;
declare @xyz int;
declare @newmarks int;
declare @oldmarks int;

select @studentid=i.student_id from inserted i; --to fetch inserted values
select @marks=i.marks from inserted i;

 
 
begin
   if update(marks)
   --set  @oldmarks=@mark
	 set  @newmarks=@marks 
	 
	  
	 insert into data1(student_id,new_marks,old_marks,date)
values (@studentid,@newmarks,@oldmarks,getdate());
end
go