Because ABCD is a rectangle, the length of CD is 12 cm.
We need to determine the length of DE. If we can do that, then the sum of the lengths of CD and DE represents the unknown: the length of CE.
To find the length of CE, we have to "solve" the upper triangle.
Here's an outline of what to do:
1. Show that BC=AD and find the length. 2. Note that angle CAD is 60 degrees. Why? 3. Note that angle EAD is 30 degrees. Why? 4. Find the length of ED 5. Add ED and DC, that is, ED + 12 cm. This is your answer.
