Oooh. Not easy.... because the ANSWER is given as a TIME... NOT a DISTANCE. I think it could be either! I'd like other opinions! How far is it? is probably the answer required. = distance How long is it? is possible but as one is talking about TIME (probably) one usually asks, "How long does it take to get from your school to home?" = time Sometimes we leave words out that we think we don't need! So, "How long does it take to get from here to there?" might get shortened to, "How long is it from here to there?" BUT you NEED the context that TIME is being discussed. If the context is clearly distance/length then How long is it? is asking about the length. How long is your swimming pool? How long is it? 25 metres? I OFTEN REPLY TO A QUESTION OF DISTANCE WITH A TIME. "HOW FAR IS IT FROM THE HOTEL TO THE BEACH?" "OH, ONLY 5 MINUTES' WALK." SO YOU WILL UNDERSTAND THAT I THINK THE MISSING WORD IS 'FAR' EVEN THOUGH THE REPLY IS GIVEN AS A TIME. And you'll also understand that I'm not entirely happy with the question, "How long is it from your school to home?" and would prefer to word it as, "How long does it take?" But you'll also realize I might actually ask, "How long is it?" (meaning time) if I'm being lazy, cutting out words, and I know that the other person knows I'm talking about time. Ha!

Moira has given you a good, complete answer. In general, people ask “how far”, and the response could involve using time to state the distance. For example, “a ten-minute walk” (or “ten minutes’ walk) is a *walk* of a certain length, but it answers the question of how far (i.e. distance). In my opinion, if your question is from some sort of exercise book, you should consider throwing that book into the trash.

Although in some cases they can be used in both situations both for time and to determine distances.

How far is usually referring to the distance of a location or object. How long is usually referring to a time.