An express train and a local train leave Pittsburgh for Washington, D.C. on the same route. The express takes $4$ hours; the local takes $5$ hours. The express is $12$ mph faster than the local. What is the speed of the **local** train?

Let $r$ be the local train's speed. Then the express is $r + 12$. Since both trains cover the **same distance** (same route, same endpoints), set the distances equal: $5 r = 4 (r + 12)$. Expand: $5 r = 4 r + 48 \Rightarrow r = 48$. So the local train's speed is $\boxed{48}$ mph (and the express runs at $60$ mph). Check: local covers $48 \times 5 = 240$ miles; express covers $60 \times 4 = 240$ miles ✓. - Trap D ($60$) is the **express** speed, not the local. Read which the question asks for. - Trap A and B give different rate combinations that don't satisfy both constraints.