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You didn't include the picture (triangle BAC and triangle FEG. First image.)
The answer I got is 5.7
My work is written out in the second image
The length of DE 21.26029163 units
Answer: 
<u>Subtract 4 from both sides</u>
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<u>Divide both sides by 3</u>
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Answer:
Step-by-step explanation:
Use the Pythagorean theorem to find the altitude.
h^2 = 9^2 - 6.4^2
h^2 = 40.04
h = 6.328
area = base * height/2
area = (2 * 6.4) * 6.328/2
area = 40.5 square units