Two line segments divide the triangle into three triangles and a quadrilateral. As shown in the figure, if the areas of the three triangles are 3, 7 and 7 respectively, the shadow area is?

∵ △ EFC = △ FCB, ∵ e to CD distance is equal to B to CD distance, ∵ DF / CF = 3 / 7, BF = EF
7△ADF=3(△AEF+7)
△AEF=△ADF+3
△ADF=7.5,△AEF=10.5,ADEF=18

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