A hexagon can be broken down into 6 equilateral triangles of side r, where r is the radius of the circumscribed circle. The height of each triangle is r√3/2 and half the base is r/2, making the area of each triangle r^2√3/4. Since there are six of these the total area is 6r^2√3/4=3r^2√3/2. If r=6, area=54√3=93.53 sq cm approx.
(The height of the triangle can be found using Pythagoras: √(r^2-(r/2)^2)=√(3r^2/4)=r√3/2.)