Context: Triangle with base angles $70°$ and $50°$, two sides extended at top vertex. Find $x$ (angle between the extensions).

Answer: B: $120$

Why: $x$ is an exterior angle at the top vertex. By the exterior angle theorem: $x = 70 + 50 = 120$. (Or: interior angle at top $= 180-70-50 = 60°$; the vertically opposite angle between extensions $= 180 - 60 = 120°$.)

Traps: A ($110$) miscalculates. C ($130$) wrong. D ($140 = 70 \times 2$) doubles one angle.