Write SQL query to solve given problem: Based on image 5, what is the percentage of images that belong windows object class?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT CAST(COUNT(T1.OBJ_SAMPLE_ID) AS REAL) * 100 / COUNT(CASE WHEN T1.IMG_ID = 5 THEN 1 ELSE 0 END) FROM IMG_OBJ AS T1 INNER JOIN OBJ_CLASSES AS T2 ON T1.OBJ_CLASS_ID = T2.OBJ_CLASS_ID WHERE T2.OBJ_CLASS = 'windows'