create table tt ( 
  ln  int, 
  pl  int, 
  id  int, 
  qty int, 
  tqty int,  
  tax varchar2(15), 
  td  date 
)

Insert into TT 
   (LN, PL, ID, QTY, TQTY,  
    TAX, td) 
 Values 
   (1, 9, 23149, 6, 1,  
    'Non-Taxable', TO_DATE('1/8/2018', 'MM/DD/YYYY'))

Insert into TT 
   (LN, PL, ID, QTY, TQTY,  
    TAX, td) 
 Values 
   (1, 9, 23149, 6, 2,  
    'Taxable', TO_DATE('11/15/2017', 'MM/DD/YYYY'))

Insert into TT 
   (LN, PL, ID, QTY, TQTY,  
    TAX, td) 
 Values 
   (1, 9, 23149, 6, 1,  
    'Taxable', TO_DATE('10/16/2017', 'MM/DD/YYYY'))

Insert into TT 
   (LN, PL, ID, QTY, TQTY,  
    TAX, td) 
 Values 
   (1, 9, 23149, 6, 1,  
    'Non-Taxable', TO_DATE('9/16/2017', 'MM/DD/YYYY'))

Insert into TT 
   (LN, PL, ID, QTY, TQTY,  
    TAX, td) 
 Values 
   (1, 9, 23149, 6, 2,  
    'Taxable', TO_DATE('5/2/2017', 'MM/DD/YYYY'))

COMMIT

SELECT * 
FROM (SELECT ln, 
       pl, 
       id, 
       qty, 
       tqty, 
       tax, 
       td 
       ,SUM(tqty) over (partition by pl ORDER BY td DESC) as CUMULATIVE_QTY  
       FROM tt 
       )  
WHERE 1=1 --cumulative_qty <= qty 
ORDER BY ln, td DESC