Need help with index to improve speed for this sql:

Hi,

i need help to get index that improve speed of this sql if possible(from our erp system, we cannot change it itself):
(it returns ~ 200 rows out of
       DOK   1566772
    DOKKAP   1601693
    DOKPOS  11196353
       ART      9276
INMANPROCUREMENTTYPE 0)

SELECT   COUNT(*) AS FUNCTIONVALUE
FROM     DOKPOS,
         DOKKAP,
         DOK,
         ART,
         INMANPROCUREMENTTYPE
WHERE    (DOKPOS.DOKART LIKE 'AB%' AND DOKPOS.DOKART ='AB'
AND DOKPOS.PRDPRDNR = 0
AND ART.SALESITEMTYPE ='R'
AND DOK.STATUS IN ('D')
AND (DOKPOS.INMANPROCUREMENTTYPEOID = 0 OR INMANPROCUREMENTTYPE.TYPECODE = 1)
AND DOKPOS.NODELIVERY = 0 AND (ART.AANR = 120 OR ART.AANR = 121))
AND DOKPOS.ARTNR=ART.ARTNR
AND DOKPOS.INMANPROCUREMENTTYPEOID=INMANPROCUREMENTTYPE.OBJECTID(+)
AND DOKPOS.DOKART=DOKKAP.DOKART
AND DOKPOS.DOKNR=DOKKAP.DOKNR