Question 1160206
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88 + 99 + (n-2)*163 = (n-2)*180


88 + 99 + 163n - 2*163 = 180n - 2*180


88 + 99 - 2*163 + 2*180 = 180n - 163n


221 = 17n


  n = 221/17 = 13.


<U>ANSWER</U>.  13 sides.
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Solved.