Question 1203444
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Apparently one of the tutors in preparing his response erased the original question....<br>
But tutor @ikleyn repeated the question in her response, so I can see what the question was.<br>
If E is the midpoint of DF, then DE (= DF - EF) is equal to EF.  Given EF = x+9 and DF = 3x+9, we have<br>
(3x+9)-(x+9) = x+9
2x = x+9
x = 9<br>
And the length of DF is 3x+9 = 3(9)+9 = 27+9 = 36.<br>
ANSWER: DF = 36<br>