Erika wants to prove that the sum of the angles in the triangle lmn is 180°. the image below is used in her proof. a triangle is shown with the angles m and n at the base and angle l at the vertex. line segments mn, lm, and ln extend past the vertices of the triangle. a line is constructed through point l that is parallel to side mn. the angles around angle l are labeled clockwise as l, 3, 2, 1, 4, and 5. to continue the proof, erika's next logical step it to prove that angle is congruent to angle n and angle is congruent to angle m. 1, 2 2, 3 3, 4 4, 5