How to sum all the returned rows

Here is a solution that uses analytics to prevent having to do two scans of mv_aeven. It does require more CPU to save the disk access and is a bit more complex, so you will have to weigh it accordingly.

SELECT * FROM
(
  SELECT a.eventnum, sum(a.num_cust), sum(a.out_minutes), a.off_dts, max(a.restore_dts)
     , a.cause, a.feeder, a.DEV_NAME
  FROM mv_outage_duration a
  WHERE a.DEV_NAME = 'T007F12127'
  GROUP BY a.eventnum, a.off_dts, a.cause, a.feeder, a.DEV_NAME
) a
INNER JOIN 
  (
  SELECT Num_1, xpers, weather_code, completion_remarks FROM 
     (
     SELECT Num_1, xpers, weather_code, completion_remarks, rev_num
        , max(rev_num) OVER (PARTITION BY Num_1) max_rev
     FROM mv_aeven
     )
  WHERE rev_num = max_rev
  ) d
ON d.Num_1 = a.eventnum;

SQL Fiddle (Includes column type definitions).

You want to make an outer join. In Oracle 8i one has to use the (+) notation.

SELECT H.STUDENT_CODE,
   H.FIRSTNAME,
   H.LASTNAME,
   H.PROGRAM,
   H.TEACHER_CODE,
   H.COUNTRY_CODE,
   AC.COUNTRY_NAME,
   P.PROGRAM_NAME,
   T.TEACHER_NAME
FROM HTUD H,
     PROGRAM P,
     TEACHER T,
     AP_COUNTRY AC
WHERE H.FIRSTNAME LIKE '%ark%'
    AND H.PROGRAM = P.PROGRAM
    AND H.TEACHER_CODE = T.TEACHER_CODE(+)
    AND H.COUNTRY_CODE = AC.COUNTRY_CODE(+)
ORDER BY H.STUDENT_CODE ASC 

Starting with Oracle 10g xou can use the ANSI join syntax,too

SELECT H.STUDENT_CODE,
   H.FIRSTNAME,
   H.LASTNAME,
   H.PROGRAM,
   H.TEACHER_CODE,
   H.COUNTRY_CODE,
   AC.COUNTRY_NAME,
   P.PROGRAM_NAME,
   T.TEACHER_NAME
FROM HTUD H JOIN PROGRAM P ON (H.PROGRAM = P.PROGRAM)
    LEFT OUTER JOIN TEACHER T ON (H.TEACHER_CODE = T.TEACHER_CODE)
    LEFT OUTER JOIN AP_COUNTRY AC ON (H.COUNTRY_CODE = AC.COUNTRY_CODE)
WHERE H.FIRSTNAME LIKE '%ark%'
ORDER BY H.STUDENT_CODE ASC