What is the longest business time on Mondays for a Yelp_Business under the category "Shopping"?
longest business time refers to max(subtract(closing_time, opening_time)); on Mondays refers to day_of_week = 'Monday';  category "Shopping" refers to category_name = 'Shopping'
SELECT T1.closing_time + 12 - T1.opening_time AS "hour" FROM Business_Hours AS T1 INNER JOIN Days AS T2 ON T1.day_id = T2.day_id INNER JOIN Business AS T3 ON T1.business_id = T3.business_id INNER JOIN Business_Categories AS T4 ON T3.business_id = T4.business_id INNER JOIN Categories AS T5 ON T4.category_id = T5.category_id WHERE T2.day_of_week LIKE 'Monday' AND T5.category_name LIKE 'Shopping' ORDER BY T1.closing_time + 12 - T1.opening_time DESC LIMIT 1