By using trigonometry
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you must know more information. Like the lengths of 2 sides. Then using Trig (law of sines or law of cosines) you can find the remaining sides and angles.
The sum of the angles in a quadrangle is 360 degrees, whatever the side lengths.
Too broad of a question... What measure are you talking about? angles? side lengths?
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they can be, depending on the information that you are given. If you know lengths of sides, then YES.