Umm, That's A lot Of Homework...
Both are correct.
Good job!

Putting the value of Y = 15

So, X = 200
ΔADC ≅ ΔBCD (SAS congruency)
∠AED ≅ ∠BEC (opposite angles)
ΔAED ≅ ΔBEC (ASA congruency)
Therefore DE <span>≅ CE (corresponding sides of the two congruent triangles AED and BEC)</span>