"It took twenty days."
the はつか comes from old Japanese readings, it's kind of an exception. A lot of dictionaries will state that the correct reading is always はつか、however, the number of people using にじゅうにち is also increasing (especially between the young), so maybe in the future? For now stick to はつか though.
です is technically a [copula](https://en.wikipedia.org/wiki/Copula_(linguistics)#Japanese), but it is often translated using a form of "to be".