ACE

Moderator note:

You should include an explanation of your steps, otherwise no one will be able to understand how you arrived at your equation.

I believed you used a circle which circumscribes the regular pentagon. If the center is $O$ , then $\angle AOE = \frac{360^\circ }{2} = 72^\circ$ and hence $\angle ACE = \frac{72^\circ}{2} = 36 ^ \circ$ .