Answer:
Step-by-step explanation:
I'm not quite sure what book your question is referring too, but the statement would probably be justified in a similar way.
For a whole day i was puzzled over the problem... = This means that the character has a problem, and they need a solution. To justify it you just need to address what problem the character is facing.
...and my faith in people was shaken = This part of the statement probably means the character may have shared a secret and it got out, or some people were just being cruel, ect. You would just need to find what happens in the story before this statement to make this character feel this way.
Hope this helps. Let me know if you have any questions.