Not sure I get the point of the trick question.
It should be clear that you can restore to ANY point in time (at each 15 minute interval in this example). However, restoring to the 9:30 state will not recover your TRUNCATEd table ... so was that thrown in as a red herring ?
If so, it got me ...
Hi - I think you may have overthought things a bit - it wasn't meant to be a complicated or trick question, but just to find out if people thought that TRUNCATE TABLE somehow affected the validity of the transaction log. It doesn't.
Thanks for the feedback though, maybe I should have made the question clearer somehow.