A chain of four circles centered at A, B, C, and D are touched on one side by the line GH and on the other side by a circular arc EF centered at O. Find the area of D in terms of the areas of A, B, and C.

Image:

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The hint is to find the relationship between the radii of those circles and to convert them to their areas. Would it have anything to do with the formula for their common external tangents ?