CREATE TABLE table_29050051_3 (_number NUMBER, position VARCHAR2, previous_school VARCHAR2)

What is the highest number a guard from brophy college prep wore?
SELECT MAX(_number) FROM table_29050051_3 WHERE position = "Guard" AND previous_school = "Brophy College Prep"
SELECT MAX("_number") FROM "table_29050051_3" WHERE "Brophy College Prep" = "previous_school" AND "Guard" = "position"