Table: vukovar_ethnicity
Columns: year_of_census
total
croats
serbs
others

Question: What is the average total of the census after 1971 with 10,412 (32.88%) Serbs?
SQL: SELECT AVG("total") FROM vukovar_ethnicity WHERE "year_of_census" > 1971 AND "serbs" = '10,412 (32.88%)'