question: what is the average water sqmi with a population (2010) more than 47 in the Brenna Township with Longitude less than -97.171507
answer: SELECT AVG(water__sqmi_) FROM table_name_8 WHERE pop__2010_ > 47 AND township = "brenna" AND longitude < -97.171507
context: CREATE TABLE table_name_8 (water__sqmi_ INTEGER, longitude VARCHAR, pop__2010_ VARCHAR, township VARCHAR)