Clean and Easy Solution :)
\n\n# Code\n\n/* Write your PL/SQL query statement below */\n\nSELECT machine_id, ROUND(SUM(CASE WHEN activity_type = \'start\' THEN -timestamp ELSE timestamp E
\n\n# Code\n```\n/* Write your PL/SQL query statement below */\n\nSELECT machine_id, ROUND(SUM(CASE WHEN activity_type = \'start\' THEN -timestamp ELSE timestamp END) / COUNT(DISTINCT process_id), 3) processing_time\nFROM Activity\ngroup by machine_id\n\n```
['Oracle']