AMC8 1997 Problem 12

[system]

\angle 1+\angle 2=180^{\circ}.
\angle 3=\angle 4.

Find \angle 4

Answer Choices
A. 20^{\circ}
B. 25^{\circ}
C. 30^{\circ}
D. 35^{\circ}
E. 40^{\circ}