To find d, you know that the other side is equal to 90. Because two sides that are opposite of each other must be equal to 180, you do 180-90 which is 90 to get d. Therefore, d=90 degrees. 99 degrees and e are alternate interior angles so that means they have to be the same. Because f is on the other side of 99 degrees and two sides that are opposite of each other must equal 180 degrees, you have to do 180-99 which is equal to 81 degrees. Therefore, d=90 degrees, e=99 degrees, and f=81 degrees
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