Thank you for your help. There are some more sentences concerning the preposition 'in.'
1. He will be back in a few days.
2. The show starts in an hour.
3. Do you wnat to meet here in an hour?
(Does 'in ' mean 'after a particular length of time'?)
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4. She learnt to drive in three weeks.
5. You can not get to the station in two hours.
6. You are not allowed to stay here in a week.
7. You can not solve the math problem in ten mimutes.
8. Don't come home in two hours.
(Does 'in' mean 'within' in the five sentences?)
How can we distinguish the two usage?
"in" means ...
1. within
2 and 3. almost exactly an hour from now
4, 5, 7, and probably 8. within
6 and 8 don't really make much sense.
6 would make better sense if you wrote this: You are not allowed to stay here for a week (or during this week). (meaning that after the week is over, you can stay here)
8 would make better sense if you wrote this: Come home in two hours. (meaning "within two hours")