Database: food_inspection_2
Question: What is the percentage of restaurants that paid a fine of 250 among all establishments?
SQL: SELECT CAST(COUNT(CASE WHEN T3.fine = 250 THEN T1.license_no END) AS REAL) * 100 / COUNT(T1.license_no) FROM establishment AS T1 INNER JOIN inspection AS T2 ON T1.license_no = T2.license_no INNER JOIN violation AS T3 ON T2.inspection_id = T3.inspection_id WHERE T1.facility_type = 'Restaurant'