Average Time of Process per Machine

Task: Find the average time each machine takes to complete a process. Result should have machine_id and processing_time (rounded to 3 decimal places).

Table: Activity

+---------------+-------------+
| Column Name   | Type        |
+---------------+-------------+
| machine_id    | INT         |
| process_id    | INT         |
| activity_type | varchar(10) |
| timestamp     | float       |
+---------------+-------------+

Input: Activity table:

+------------+------------+---------------+-----------+
| machine_id | process_id | activity_type | timestamp |
+------------+------------+---------------+-----------+
| 0          | 0          | start         | 0.712     |
| 0          | 0          | end           | 1.52      |
| 0          | 1          | start         | 3.14      |
| 0          | 1          | end           | 4.12      |
| 1          | 0          | start         | 0.55      |
| 1          | 0          | end           | 1.55      |
| 1          | 1          | start         | 0.43      |
| 1          | 1          | end           | 1.42      |
| 2          | 0          | start         | 4.1       |
| 2          | 0          | end           | 4.512     |
| 2          | 1          | start         | 2.5       |
| 2          | 1          | end           | 5         |
+------------+------------+---------------+-----------+

Output:

+------------+-----------------+
| machine_id | processing_time |
+------------+-----------------+
| 0          | 0.894           |
| 1          | 0.995           |
| 2          | 1.456           |
+------------+-----------------+