OG详解-OG1 数学2 Q13

The correct answer is 70. Based on the figure, the angle with measure 110° and the angle vertical to the angle with measure x°  are same side interior angles. Since vertical angles are congruent, the angle vertical to the angle with measure  also has measure x°. It’s given that lines s  and t are parallel. Therefore, same side interior angles between lines s  and t are supplementary. It follows that x +110 = 180. Subtracting 110 from both sides of this equation yields x = 70.