In the given figure, two parallel lines are intersected by a transversal. Find the measure of angle $y$. 
A$102^{\circ}$
B$118^{\circ}$
C$128^{\circ}$
D$154^{\circ}$
Answer & Solution
Correct answer: C. $128^{\circ}$
The labelled angles $2x$ and $3x+50^{\circ}$ are supplementary because they lie on the same side between parallel lines. So $2x+(3x+50^{\circ})=180^{\circ}$, giving $5x=130^{\circ}$ and $x=26^{\circ}$. Angle $y$ is vertically opposite to the angle measuring $3x+50^{\circ}$, so $y=3(26^{\circ})+50^{\circ}=128^{\circ}$. The tempting wrong choice $118^{\circ}$ comes from arithmetic error in substituting $x$.
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