Thank you for the opportunity to help you with your question!
Always remember that the order of the letters tells us the measure of each part. EC is the same as BC because of where they appear in the name of the triangle (^ABC = ^ DEC). Now, if we figure out BC, we at the same time find EC since they are the same. BC is 12, so EC is also 12.
Please let me know if you need any clarification. I'm always happy to answer your questions.