From my diagram, you can see that the folded figure is a square because all the sides are equal.
Hence the two diagonals are 20 cm which means the radius of the quadrant is 20cm.
Area of quadrant = (πr2 ) / 4 = (3.14 x 20 x 20) / 4 = 314
Area of the square = (1/2) b x h x 4 = 1/2 x 10 x 10 x 4 = 200 (made up of 4 right angled triangles)
Hence area of shaded part = 314-200 = 114cm2
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