CREATE TABLE table_name_45 (date VARCHAR, site VARCHAR, opponent VARCHAR)

What is the Date at memorial stadium minneapolis, mn, and an Opponent of northwestern?
SELECT date FROM table_name_45 WHERE site = "memorial stadium • minneapolis, mn" AND opponent = "northwestern"
SELECT "date" FROM "table_name_45" WHERE "memorial stadium • minneapolis, mn" = "site" AND "northwestern" = "opponent"