Database: food_inspection_2
Question: Among the establishments that failed in the inspection, what is the percentage of establishments with the highest risk level?
SQL: SELECT CAST(COUNT(CASE WHEN T1.risk_level = 3 THEN T1.license_no END) AS REAL) * 100 / COUNT(T1.risk_level) FROM establishment AS T1 INNER JOIN inspection AS T2 ON T1.license_no = T2.license_no WHERE T2.results = 'Fail'