Check the picture below.
we know BC ≅ CE due to the midpointness of C.
we know AB ≅ DC, since it's given.
because AB || DC, each of those segments are going to hit the segment BE at the same angle of elevation, or namely ∡CBA = ∡ECD, and since that's the case then each triangle has a Side Angle Side that's congruent with the other triangle, SAS.
