People complain that it takes so long to get things addressed through these reports. This is such an odd way to say this in English, yes it's proper English, but really, who would say it this way? I feel like people get excited if they find some odd case that is proper English but not accepted so they can report it.
I'd prefer the Duo team spend their time fixing real errors in the translations rather than addressing these extreme corner cases.
I feel like the main purpose of this exercise is to show us that in Spanish they put the preposition at the front of the sentence although we typically would not in English. It's the same with "A qué hora sales de casa" sure you could say At what time do you leave home, but that misses the whole point. The whole point, to me at least, is to show the student that although we say what time do you leave home, you need to use the "A" in Spanish. That way our brains will start to connect and remember that A qué hora = What time and so when you one day have to think, ok I need to ask someone what time something, you will automatically think ok what time = a que hora. In your answer you're tying a phrase "In what city" to it's Spanish counterpart in your brain, but when will you ever think of a sentence that begins with "In what city" to ever be able to use that information?