The answer is 45, I can't put a explanation but if you want one reply.
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tan∠EFA = 30 / 18
DG = tan∠EFA * DF
[DGF] = 30 cm2
or
18 / 30 = 6 / DG
DG = 10
[DGF] = 1/2(10 * 6)
Yes I agree with IhaveOBJD, there's no possible way for DGF to be 30, 30 = AB or BC or CD or AD, not DGF area.
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