The sum of the measures of an exterior angle of a polygon is 360°.
If the given angle divides 360 evenly, then it can be a measure of an exterior angle of a polygon. If otherwise, then it cannot be.
[tex]\begin{gathered} 360\div30=12 \\ 360\div50=7.2 \\ 360\div120=3 \\ 360\div90=4 \\ 360\div40=9 \end{gathered}[/tex]
Out of the given angles, only 50 does not divide 360 evenly. Therefore, a regular polygon cannot have an exterior angle measuring 50°. (Option B)
