This exercise is from Raymond Murphy's "English Grammar in Use". It's about the use of "could have done."
"Read this information about Ken:
Ken didn't do anything on Saturday evening.
Ken doesn't know anything about machines.
Ken was free on Monday afternoon.
Ken was short of money last week.
Ken's car was stolen on Monday.
Ken had to work on Friday evening.
Some people wanted Ken to do different things last week but they couldn't contact him. So he didn't do any of these things. You have to say whether he could have done or couldn't have done them.
- Ken's aunt wanted him to drive her to the airport on Tuesday.
Answer: He couldn't have driven her to the airport (because his car had been stolen).
Etc.
The idea is that it would not have been possible for Ken to drive his aunt to the airport, even if she had been able to contact him. "Could" is not correct.
But if I change the situation and say "He could drive his aunt to the airport after he had fixed the car."
Is this situation understood as a particular situation in which using "could" is wrong and should I use "he was able to drive her" or "he managed to drive her"?
"He couldn't drive his aunt to the airport" is correct only if I mean -he wasn't able to drive his aunt to the airport but not if I am saying "he wouldn't have been able to drive her. If I remove "could not" from it and use "wasn't able to drive" or "did not manage to drive.." it wouldn't be wrong, right?