Translation:There are three chairs in this office.
A funny fact about this sentence. The audio version in normal speed contains numeral "dvě", but slow version contains numeral "tři". It is impossible to catch it even by native speakers.
As a slavic-language-speaker (Ukrine), I hear "tři". The other problem, that I also hear kancelářE, instead of kancelářI... (damn, lost my last heart to skip this lesson on this)
The answer "In this office are three chairs" should also be accepted.
I have added "Three chairs are in this office," since similar sentences would be fine. For example: Three books are on this desk -- Four people are on this boat -- Two cats are on this windowsill.
'In this office are three chairs' is still not accepted. Is there a problem with this interpretation.
"In this office are three chairs" sounds awkward, as would similar sentences like: On this desk are three books -- On this boat are four people -- On this windowsill are two cats. To my native (AmE) ear, it sounds like we should be contrasting something. For instance, "In THIS office there are three chairs, but there are six chairs in THAT one." So I'm not inclined to add this word order at this time.