Also in the mark scheme there is a question on a polygon where the answer is a dodecagon and don't understand it :
The triangle is an equilateral one, which means all the sides are equal, and all the angles = 60 degrees each. If you split the top angle in the triangle,it would become 30 degrees and would be the exterior angle of the shape. If you know the exterior angle is 30 degrees, you can work out the number of sides, simply by dividing 360 by it, so 360/30= 12, so the shape is 12 sided. A 12 sided shape is known as a dodecagon. Hope that helps.