SQL & PL/SQL :: Required Expected Output Using Decode

Oracle version : Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod

create table plc_dw_dry_run_fic_rfsh (dry_run_fic_id number,ltr_code varchar2(10),
next_cpn_lvl_id1 number,next_intrvl_code varchar2(10), next_intrvl_value varchar2(120));

begin
insert into plc_dw_dry_run_fic_rfsh values (424740,'1','','LTML','48000');
insert into plc_dw_dry_run_fic_rfsh values (424736,'1','','LTML','32000');
insert into plc_dw_dry_run_fic_rfsh values (424738,'1','','LTML','128000');
insert into plc_dw_dry_run_fic_rfsh values (424783,'1','','LTML','96000');
insert into plc_dw_dry_run_fic_rfsh values (424789,'2','','LTML','96000');
insert into plc_dw_dry_run_fic_rfsh values (424750,'1',198,'LTML','10000');
insert into plc_dw_dry_run_fic_rfsh values (424760,'1',199,'LDFM','20000');
insert into plc_dw_dry_run_fic_rfsh values (424770,'1','','LTML','192000');
end;

commit;

Expected output
---------------
DRY_RUN_FIC_ID LTR_CODE NEW_LTR_CODE
424740 '1' '1b'
424736 '1' '1'
424738 '1' '1'
424783 '1' '1a'
424789 '2' '1a'
424750 '1' '1a'
424760 '1' '1a'
424770 '1' '1a'

Rules
---------
1) First next_cpn_lvl_id1 should be considered (next_intrvl_code can be anything), if next_cpn_lvl_id1 is 198 or 199 then new_ltr_code should have 1a.

2) If next_cpn_lvl_id1 is not 198 or 199, then next_intrvl_code should be considered

a) if next_intrvl_code is LTML and mod of next_intrvl_value and 96000 is zero then new_ltr_code should be 1a
b) if next_intrvl_code is LTML and mod of next_intrvl_value and 48000 is zero then new_ltr_code should be 1b

3) If 1 & 2 are not satisfied, ltr_code should be assigned to new_ltr_code.