BE is parallel to CD, therefore, m∠BEC=m∠ECD, therefore mBC=mDE BE is the diameter, so Arc BE is 180 degree mBC+mCD+mDE=180 replace mCD with 3mBC, and replace mDE with mBC: mBC+3mBC+mBC=180 5mBC=180 mBC=180/5=36 mCD=3mBC=3*36=108 the inscirbed angle m∠ECD= the measure of arc DE=36
