How many restaurants were inspected on 2015/5/8?
restaurant refers to facility_type = 'Restaurant'; on 2015/5/8 refers to inspection_date = '2015-05-08'
SELECT COUNT(T2.license_no) FROM establishment AS T1 INNER JOIN inspection AS T2 ON T1.license_no = T2.license_no WHERE T2.inspection_date = '2015-05-08' AND T1.facility_type = 'Restaurant'