CREATE TABLE table_name_28 (enrollment_08_09 INTEGER, previous_counference VARCHAR(255), ihsaa_class VARCHAR(255))
What is the average enrollment 08=09, for the team that had a previous conference of lake and IHSAA class of 3A?
    
SQL: SELECT AVG(enrollment_08_09) FROM table_name_28 WHERE previous_counference = "lake" AND ihsaa_class = "3a"