Lines, angles, and triangles SAT question

The correct answer is $70$. Based on the figure, the angle with measure $110^{\circ }$ and the angle vertical to the angle with measure $x^{\circ }$ are same side interior angles. Since vertical angles are congruent, the angle vertical to the angle with measure $x^{\circ }$ also has measure $x^{\circ }$. 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 $x=70$.