"How many hours do they work?"
It seems to be in Japanese now, but sometimes that bug crops up with sentences and needs to be reported: https://support.duolingo.com/hc/en-us/articles/204728264-How-do-I-report-a-bug-
You're reading the comment through the lens of knowing that Android doesn't allow listening from the sentence discussion. We're all reading the comment through the lens of the person is posting in the sentence discussion asking how to open the sentence discussion. We're coming from different viewpoints that led to confusion. If we don't all have the same information, we don't come to the same conclusion. Trying to understand where another person is coming from is an important part of communicating on this forum, which is why I appreciated the information that you posted about Android users not having access to audio playback.
@IsolaCiao : Yes they did ask to how to open the sentence discussion... but why? In order to listen to the audio. Read again.
How do you open the sentence discussion (on an android)? I have so often thought this would be helpful, to be able to hear the correct answer!
【かれ -らは・なん -じかん・はたらきますか？】
more about the ～時間 counter here:
働きます (hatarakimasu) is the verb for "to work/labor"
仕事をします (shigoto wo shimasu) is shigoto (noun: work/job) and shimasu (verb: to do), so literally "To do my job"
They can be interchangeable in some cases but hatarakimasu is a general work and shigoto wo shimasu is more specifically a job or business
The context of a topic is heavily required when deciding who is being spoken about or of. If you were having a conversation about a person in particular, simply asking this question out of the blue would imply you're talking about that same person. If you said it as a complete conversational pivot (i.e. you mention this when talking to someone else about themselves), even though you meant it about a different person, it would be implied that it was directed to the person you're talking to. "彼ら" can only be omitted if it's clear who you're talking about, which context provides.
I'm a bit confused. If "Nani" literally means "what", and "nanjikan" is literally "hours", why/how does it turn into "how many hours" and not "what hours"? Am I possibly looking into this too much, and it's just a matter of looking at a literal translation, or is there a science behind it?
はたらきます is an intransitive verb, which means that it never has a direct object and cannot take the を particle. You can check transitive vs. intransitive verbs by checking the word in the dictionary (eg Jisho.org). (Minor exception: intransitive motion verbs can take を if the location involved in the motion is the direct object.)
いつ is "when/how soon"
You could use that for "When do they work" asking for a specific time they start working, but here you're specifically asking "what span of hours do they work",
There is more than one way to ask "how many" in Japanese, but typically you use the counter for the specific thing you want to ask about, prefixed with 何 where the amount would go when counting
何冊 - what number of volumes
何人 - what number of people
何時間 - what number of hours
For numbers that are counted with the counter つ (using the native Japanese numbers rather than Sino-Japanese like most counters do) you use いくつ instead of 何つ
テーブルはいくつありますか how many tables are there?
テーブルが三つあります - there are three tables
Not quite; You've combined two question words into one there,
何時間 - How many hours (時間 is a counter for hours, you'd get a reply of something like 三時間・さんじかん "three hours")
いくつ - How many things (つ is a general counter for things, you'd get a reply of 三つ・みっつ "three things")
So it reads something like "How many things hours do they work"
はたらきます is an intransitive verb, which means you cannot use を with it because it has no direct object.
Think of transitive/action verbs like "to eat" or "to drink." They have a very clear direct object that you're performing the action on. In contrast, "to work" isn't performing the action on anything in particular.
In normal, everyday Japanese there are no spaces. It may seem like one giant word, but because there are kanji, hiragana, and katakana, it's usually easy to intuit where one word stops and another begins. In children's books where everything is written in hiragana there are often spaces after some words to make it easier to read.
The kanji 間 is a gap or span, combined with time/the hour counter 時, 時間 marks a period/length of time. So the question is more "What length of time/hours do they work". Which gets more comfortably simplified to "how many hours" in English.
Without it 彼らは何時働きますか would mean "What time/hour(s) do they work"
That would be "how much do they work?", versus the Duolingo question specifically asking "how many hours do they work?"
No. Japanese uses a system of counter words (typically based on the size/shape of the thing you're counting), and "how many" is translated differently, based on the counter. いくつ is used when the counter is つ, but many (most?) are 何+counter. 時間 is the counter for hours of duration, and "how many" is translated as 何時間 when that is the counter used.