an angle of a regular polygon is given by a formula \(\frac{(n-2)*180}{n}\)
Hence we have y = \(\frac{(n-2)*180}{n}\)
here, \(n\) = no of sides of the polygon
\(X\) here is an external angle of the polygon

external angles of a regular polygon add up to 360 degrees
therefore \(x = 360/n\)
Given that,
\(y = 5X\)

\(5X =\) \(\frac{(n-2)*180}{n}\)

\(5X*n = (n-2)*180\)

\(5* 360 = (n-2)*180\)

solve for n; \(n = 12\)
option D
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Nice solution!