Usage of triggers(URGENT)

Hi

HAPPY NEW YEAR

This is Naina. I have an issue on use of triggers in plsql where i am posting here

i have 4 tables a,b,c,d

all the tables are having a common coloumn 'id'

now if i delete any row in any of the tables b,c,d
for ex: if i delete from b, then it should check in c,d for corresponding record with deleted row id of b and if there are no records found then it should delete the corresponding row in a

same should follow with c,d tables also

this should be done with using triggers.
Please help me out of this

Thanks and Regards
Naina