Among the films with a rental duration of 7 days, how many are comedies?
rental duration of 7 refers to rental_duration = 7; comedies refers to name = 'Comedy'
SELECT COUNT(T1.film_id) FROM film AS T1 INNER JOIN film_category AS T2 ON T1.film_id = T2.film_id INNER JOIN category AS T3 ON T2.category_id = T3.category_id WHERE T1.rental_duration = 7 AND T3.name = 'Comedy'