Angle ACB = 72 degrees
Angle BCE = 90 degrees
Angle DCE = x degrees
The three angles combine to form the straight angle ACD, which is 180 degrees
(angle ACB) + (angle BCE) + (angle DCE) = 180
(72) + (90) + (x) = 180
162 + x = 180
x = 180-162
x = 18
Angle DCE is 18 degrees
