Works out or Reckons out

Talking about technology: [...]For example, when you want to take a photograph, simply make a frame around the image with your hand and click your fingers. The device works/reckons out what you want and operates the camera.

I chose the word "reckons" but the answer says it is "works", but I don't know if it is really right.

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Hey there FELYPE,

According to the context of the text The Gesture Interface, we are talking about the features of a device. The word reckon as a verb means (1) to think or believe or (2) to consider or have the opinion that something is as stated.

It does not apply to the answer.
Not to mention that there is not a phrasal verb called reckon out in the dictionary.

The answer is work.
You can check the answer on this website: FCE Reading and Use of English Practice - Tests.

The phrasal verb to work out, in the presented context, means to be the result of a calculation or indicates a device which happens or develops in a particular, especially a satisfactory, way, or which is suitable for a particular situation.
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For example, when you want to take a photograph, simply make a frame around the image with your hand and click your fingers. The device works out what you want and operates the camera.
>> Por exemplo, quando você(s) quer(em) tirar uma foto, basta focalizar(em) um quadro ao redor da imagem com sua(s) mão(s) e clicar(em) com os dedos. O aparelho determina / identifica o que você(s) quer(em) e opera a câmera.
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I hope we've helped you :)
Enjoy your studies!