Translation:I work with computer maintenance.
No. Similarly to English, that would be ‘trabalhar no/na’.
I work in the X sector. = Trabalho no setor de X.
But watch out! ‘Trabalhar’ can also take ‘com’ just like in English:
O governo está trabalhando com o setor privado. = The government is working (together) with the private sector.
I still upvoted you because I thought it was a good question.
Sure, a literal translation would make it "with"; however, since the subject of the action is not a concrete object or group it doesn't really make sense in English. Here it should be "in". If the sentence was "I work with computers" or "In work with the computer maintenance department" then "with" can be used. As someone else points out, the given answer would work if computer maintenance was a proper noun (i.e., "I work with Computer Maintenance"). The desired answer, "I work with computer maintenance" does not treat it as a proper noun, so I don't think it should be accepted.
I just reported it. Translating does not mean translating each word of a given sentance, it means to end up with the "sound " sentance in a specific language. So even if Duo meant that somebody is working in a department which is working along "with" maintenance both answers should be accepted.