Need help Tuning Inventory SQL Script

I'm trying to tune this sql script for our Inventory PLSQL program; the procedure is very slow that it takes hours to complete. I ran a Tkprof on the program trace file and it show that there are two expensive SQL scripts and the one below is the main culprit. Any kind of help will be appreciated.

Thanks in advance.

Leo

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 SELECT msib.organization_id, msib.inventory_item_id, msib.segment1,
                msib.description, msib.planning_make_buy_code, msib.buyer_id,
                msib.planner_code, msib.primary_uom_code,
                msib.safety_stock_bucket_days,
                (SELECT NVL (cic.item_cost, 0)
                   FROM cst_item_costs cic, cst_cost_types cct