Hi Bruna! It seems like there is a mistake in the sentence. It should be, "They were tired because they had been helping on the farm all day," in which case it wouldn't be passive voice, but just past simple. Hope this helps, let me know if you have any questions!

The sentence is wrong, it should read 'they were tired' without 'been'. Yes, it is in the simple past.

Hello Bruna, This sentence is not correct. It should read: "They were tired because they had been helping on the farm all day." "They were tired..." is simple past tense. "...they had been helping..." is the past perfect continuous tense. (If the sentence began: "They have been tired..." that would be the present perfect tense and it isn't passive. But, this doesn't work with the second clause, so you would not use this structure.) I hope this helps.

the been between were and tired is not needed.