SQL query is slow.

Following SQL query is running slow:
=============================

      SELECT   a.ben_no,   '1' type_cd,   :INCOME_CD INCOME_CD,  ben_id ID,    B.FULL_NAME_A NAME   FROM   cm_ben_val_data a, cm_beneficiaries b  WHERE       a.ben_no = b.ben_no   and  cmdb.f_Get_age_yy ( b.birth_dt ,  cmdbdt.f_hijcurrrev ) >= 18  and  nvl( death_flag_cd , 0 ) = 0  AND ID_NAME_cHG_CD = 2  AND NVL (send_to_income_val, 0) = 0;
      UNION ALL
      SELECT   a.ben_no,  '2' type_cd,    :INCOME_CD INCOME_CD,  RLTV_ID ID, a.RLTV_NAME NAME FROM   cm_ben_fam_struc a , cm_beneficiaries  b WHERE  a.ben_no = b.ben_no    and  cmdb.f_Get_age_yy ( b.birth_dt ,  cmdbdt.f_hijcurrrev ) >= 18 and  death_cd = 0 and NVL (send_to_income_val, 0) = 0;