Find the area of the regular 30​-gon with radius 7 mm.

A formula to find the area of a regular polygon given the radius is:

Area  =  r² · n · sin( 360 / n ) / 2

          =  7² · 30 · sin( 360 / 30 ) / 2

          =  7² · 30 · sin( 12 ) / 2

          =  5.09 mm²     (approximately)

The area  is given by :

30 * (1/2) * (7^2) * sin (12°)  ≈   152.8 mm^2  

[ I think geno's answer would be the same.....]