Two trucks leave the same rest area at the same time, one heading east and the other west. The westbound truck averages $70$ mph; the eastbound truck averages $60$ mph. After how many hours are the two trucks $325$ miles apart?

Both trucks travel for the **same time** $t$. Their distances are different because their speeds differ, and the trucks separate at a **combined rate** equal to the sum of their speeds (because they move in opposite directions). Distance apart $= (70 + 60) t = 130 t$. Set this equal to $325$: $130 t = 325 \Rightarrow t = \dfrac{325}{130} = 2.5$ hours. Check: in $2.5$ hours, west truck covers $70 \times 2.5 = 175$ miles; east truck covers $60 \times 2.5 = 150$ miles. Total separation $= 175 + 150 = 325$ ✓. - Trap A ($2$ hours) gives only $260$ miles of separation. - Trap C ($3$) gives $390$ miles — too far. - Trap D ($5.4 = 325 / 60$) ignores the westbound truck. Key: when objects move in opposite directions, their **closing/separating speed** is the **sum** of their speeds.