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
