[tex]\bf \textit{sum of all exterior angles in a polygon}\\\\
n\theta =360\quad
\begin{cases}
n=\textit{number of sides}\\
\theta =\textit{angle in degrees}\\
----------\\
\theta =21.2^o
\end{cases}\implies n21.2=360
\\\\\\
n=\cfrac{360}{21.2}\implies n\approx 16.981132\implies n\approx 17[/tex]
the reason why the value is not an integer, is most likely because the 21.2° is just an approximation.
