А чому не "How long have you been working in the office?"

Між двома голосними має стояти прийменник "В". Репорт

Why not "How long were you working in the office" Imperfective tense. It's not known whether the work is permamently terminated or not

I don't know if it should be accepted, but a common way to say something similar is "for how long did you work from the office.". Same meaning, but maybe a different translation.