Need Help tuning this query uses 68% of execution time

 SELECT r.auto_charge_rule_name,

       r.auto_charge_rule_id,

r.flat_fee_amount,

r.eligibility_condition,

       r.FUNCTION,

r.attribute01 all_instances,

r.attribute02 rule_type,

        csc.csc_id,

csc.charge_sub_type_name,

csc.charge_type_name,

csc.enabled_flag,

        r.attribute03 allow_reversal,

r.attribute04 allow_inelig_rev,

        r.attribute05 eff_date_function,

r.attribute06 apply_matrix,

        csc.attribute03 apply_tax,

r.attribute07 earning_track

        FROM SBS_AUTO_CHARGE_RULES r, SBS_CHARGE_SUB_CHARGE_MAP csc

        WHERE TO_NUMBER (csc.attribute06) = r.auto_charge_rule_id

        AND (r.valid_to IS NULL OR r.valid_to >= SYSDATE)