check the picture below.
since we know that the quadrilaterals are similar, we can simply use proportions.
we can use corresponding sides GH and CD to get the ratio of both figures
[tex] \bf \cfrac{small~figure}{large~figure}\qquad \cfrac{GH}{CD}\implies \cfrac{12}{30}\implies \cfrac{2}{5}
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\textit{so the figures are in a ratio of }2:5\qquad therefore
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\cfrac{small~figure}{large~figure}\qquad \cfrac{FG}{BC}=\cfrac{2}{5}\implies \cfrac{FG}{40}=\cfrac{2}{5}\\\\\\ FG=\cfrac{40\cdot 2}{5}\implies FG=16 [/tex]
