Find the location of businesses that has business hours from 9 am to 9 pm every Saturday.
9 am refers to opening_time = '9AM'; 9 pm refers to closing_time = '9PM'; every Saturday refers to day_of_week = 'Saturday'; location refers to city
SELECT T1.city FROM Business AS T1 INNER JOIN Business_Hours AS T2 ON T1.business_id = T2.business_id INNER JOIN Days AS T3 ON T2.day_id = T3.day_id WHERE T2.closing_time LIKE '9PM' AND T2.opening_time LIKE '9AM' AND T3.day_of_week LIKE 'Saturday' GROUP BY T1.city