Because angle B=80 degrees (known)

Angle BME= 100 degree (two straight lines are parallel and complementary to the inner angle of the side)

Because the angle BMD=30 degrees (known)

Angle DME= Angle BME+ Angle BMD= 100+30= 130.

Because AB//CD (known)

EF//CD(A//B, A//C, then A//C)

Factor DME= 130 degrees (certified)

Angle D= 180- Angle DME= 180- 130=50 (complementary angles of two parallel lines with internal angles).

A: Angle D=50 degrees.

Hope to adopt