SQL & PL/SQL :: Insert Or Update Trigger On Table B

Select * from Table A where emp=1;
Emp AID
1 111

select * from Table B where emp=1 ;
----------
AID, emp, start_dt, End_dt
111 1 01-jan-2011 31-dec-2011
112 1 01-jan-2011 31-dec-2011
113 1 01-jan-2011 31-dec-2011

I have After insert or update trigger on Table B. This will update AID column on Table B.

after insert update on table B
update A
set AID=:new.AID where emp=:new.emp;

if i end date any record on table B i wanted to update max(AID) on Table A.

EX update table b
set end_dt= sysdate-1
where aid=111;

So I wrote the trigger on Table A as below

before insert or update on trigger A
declare
v_aid number;
v_strt_dt date;
v_end_dt date;
begin

select max(AID) from table B
where emp=:new.emp;
select v_end_dt from table B where aid=:new.Aid;
if v_end_dt<sysdate then
:new.aid:=v_AID;
end if;

But the problem here is its giving mutating error.Then i tried with autonomus transaction but it willreturn old value when it fiers.

So how can i achive both the task at a time.That means i have to endate Table A , Same time i have to update active max(AID) to table B.