Shouldn't 'kontor' be plural, i.e. 'kontorer'? To me, Swedish sounds like 'office' is singular, but the English sentence specifies plural (else it should be 'in the/en office'). Or should it be reported as a mistake?
ej is synonymous with inte, but much more formal. You'll encounter it in formal text and where brevity is important. So for that reason, we do need to accept it, even though the solution with inte is much better for most use cases.
Is there a general rule for words such as "kontor" that are written and pronounced the same regardless of whether they are singular or plural? I was trying to think of the plural for "kontor" - and after realizing there were no options - I just concluded it was the same word.