Here we have a regular hexagon i.e. a 6 sides polyhedron where all the sides have the same measures and the angles between two consecutive sides are all the same. As you can see the 6 vertices of the hexagon and the central point O form 6 equilateral triangles. Since they are equilateral all of their angles measure 60° in particular the six angles that have O as their vertex (for example: GOB, BOC, COD, etc). This means that if we perform a 60° rotation the side OC is mapped onto the place of OB and OB onto OG and so on. So basically a 60° rotation maps each vertex of the hexagon to the one right next to it. This means that C is mapped onto B after a 60° rotation. If we perform another 60° rotation then C will be mapped onto the original position of point G so basically the rotation we are looking for is the sum of two 60° rotations. Then the degree of the rotation that maps C onto G is 120°. Then the answer is 120°.