Translation:You can get there in thirty minutes.
I understand now. But then they have made a mistake. Because you can't use "ci" in the first sentence. But only in the second one. For example: 1. Sei stato nella chiesa? 2. Ci sono stato. And here ci replaces "nella chiesa". But because they put it in the first sentence, I thought they meant something else. Anyway, thanks for the explanation.
You can do that ONLY in the "second" sentence. For example: 1st sentence - Can you come to the house? (Puoi venire a casa?); 2nd sentence - Yes, I can come there. (Sì. ci posso venire). Here you can see that CI replaces "to the house". Another example: 1st sentence - Are you going to the theater? (Vai al cinema?); 2nd sentence - Yes, I am going there. (Sì, ci vado). As in the first example, CI also replaces mentioned place, house or theater. CI has multiple applications in Italian language. This is just one. Another one is for changing personal pronouns through cases. There you can use CI in the first sentence, in the beginning of the conversation. CI guardano (They are looking at us). CI replaces "at us". Or, CI da (He gives us), CI replaces "us". But, to get back to your question. "We can get there" - "Noi possiamo arrivare lì". That would be a correct answer as for the first sentence. Lì means there. Or Là. But, you want to use CI. And you can do that only as a reply to some previous question. For example: 1st sentence - Potete arrivare al mare? (Can you get to the sea?); 2nd sentence - Sì, ci possiamo arrivare. (Yes, we can get there). And only in that context. Not as the first sentence. Only as a reply to some previous question. FrancescoN41 wrote "Ci possiamo arrivare" and that is a correct answer only as a reply. This is very important, because if you use it in the first sentence, it does not make much of a sense. Hope I helped you.
I agree. For example, I ask you: "Che ne dici(1st), ci possiamo arrivare in trenta minuti ? (2nd)" what do you think about,(1st), can we arrive (there) in thirty minutes ? (2nd) "
Or: Veloci! (1st) Ci dobbiamo arrivare in trenta minuti (2nd) Hurry up! (1st) we have to get there in thirty minutes(2nd)
Ci (we) possiamo (can) arrivare (arrive "there","above","downstairs", etc.)
or impersonal construction http://forum.wordreference.com/showthread.php?t=227672
Ci si può arrivare.
In english can and able to are often interchangeable in the present. In fact I understood that potere translates "to be able". Why does Duolingo mark my translations as incorrect?. e.g. You are able to arrive there in 30 minutes. Am I missing something or is this a mistake on the part of duolingo?
I guess it didn't get entered as a possible solution because it's a sentence that would be very unlikely to be used by a native English speaker. Yes it does sense in that it's understandable, but it is not what would normally be said. In English for the same sense, we use 'You can get there in 30 minutes'