One concurrent program running for long time

Hi,

One concurrent program running for long time and i have generated tkporf , Below is the sql which is taking for long time.But when we check explain plan , cost is very low.

 db file sequential read is very high.How to tune this query for :

APPS : 11.5.10.2

Db : 10.2.0.2

SELECT /*+ optimizer_features_enable('9.2.0') */ PHA.VENDOR_ID, 

  PHA.VENDOR_SITE_ID, PHA.PO_HEADER_ID, PHA.SEGMENT1 PO_NUMBER, 

  NVL(PLL.NEED_BY_DATE,PLL.PROMISED_DATE) PO_DATE, PHA.CLOSED_CODE, 

  SUM(NVL(PLL.QUANTITY_RECEIVED,0)-NVL(PLD.QUANTITY_BILLED,0)) AMOUNT, 

  PHA.ATTRIBUTE1, PHA.ATTRIBUTE2, PHA.ATTRIBUTE3, PHA.ATTRIBUTE4,