Table schema:
CREATE TABLE table_name_28 (since_beginning_of_big_12 VARCHAR, last_5_meetings VARCHAR, last_10_meetings VARCHAR, at_neutral_site VARCHAR)

Question: what is the since beginning of big 12 when last 10 meetings is ou, 7-3, neutral site is ou, 2-1, and last 5 meetings is bu, 3-2?
SQL: SELECT since_beginning_of_big_12 FROM table_name_28 WHERE last_10_meetings = "ou, 7-3" AND at_neutral_site = "ou, 2-1" AND last_5_meetings = "bu, 3-2"