"He keeps the farm."
Translation:Ele mantém a fazenda.
I made a different mistake (mixed up manter and fazer, ooops...), but the system told me the answer was "Ele cuida da fazenda," which means "he takes care of the farm." That's another sense of "to keep," but it strike me as odd at this stage, since "cuidar" has never been introduced.
Cuidar is a valid choice as well.
Manter - to keep or to maintain (as in maintenance)
Cuidar - to take care of, to look after (as in maintenance)
The English sentence, depending on context, could mean either, he keeps the farm in order or he maintains possession of the farm.
I think Duo has chosen the first option.
If the sentence has the meaning of retaining ownership a better translation would be-
Ele fica com a fazenda