If the ending time is 10:08, and the elasped is 30 minutes

If your question is "what time was it before the elapsed time", then the answer will be 9:38. All you have to do is to deduct the time by 30 minutes based on your clock, and you will be able to get the answer right away. Also, if you add 9:38 by 30 minutes, you will get 10:08 as well.

Ending time = 10:08.

Elapsed = 30 minutes.

Start time = 10:08 - 30 minutes.

10:08 - 00:30 = 9:68 - 00:30

9:38

Therefore start time = 9:38