Answer: 10 minutes - how long since the last block
Bitcoin mining is a progress-free process, therefore the expected time to the next block is always ten minutes, regardless of how much time has passed (assuming that the difficulty matches the deployed hashrate).
I also think that you are either interpreting the question 1.c. very differently from me.
Bitcoin mining is a progress-free process, therefore the expected time to the next block is always ten minutes, regardless of how much time has passed (assuming that the difficulty matches the deployed hashrate).
I also think that you are either interpreting the question 1.c. very differently from me.