The diagram shows a decorative tile in the shape of a sector OAB OAB\,OAB of a circle with centre OOO. OA OA\,OA is the diameter of a semi-circle. OA=12OA = 12OA=12 cm.

Find the area of the shaded region (the area of the sector minus the area of the semi-circle). Give your answer in terms of π\piπ.