Table schema:
CREATE TABLE table_name_28 (enrollment_08_09 INTEGER, previous_counference VARCHAR, ihsaa_class VARCHAR)

Question: 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"