interior angles - polygons

It's a regular 12-agon so PQ and QR are equal. 

The sum of the interior angles of a polygon with n sides is (n – 2) • 180 

In this case, 10 • 180 = 1800 

There are 12 angles so one of them is 1800/12 = 150 

So angle PQR is 150^o  

The sum of the angles of a triangle is 180^o  

So the total of the two small angles is 180 – 150  =  30  

So each of the small angles is 15^o  

angle PRQ = 1/2(360 / 12)