1. **Problem 1:** Two airplanes leave St. Louis at the same time and fly in opposite directions. One travels at 500 km/h, the other at 600 km/h. Find the time $t$ when they are 1925 km apart. 2. **Formula:** Distance = Rate \times Time, or $d = rt$. 3. Since they fly in opposite directions, their distances add up: $$500t + 600t = 1925$$ 4. Combine like terms: $$1100t = 1925$$ 5. Solve for $t$: $$t = \frac{1925}{1100} = 1.75 \text{ hours}$$ 6. **Answer:** It will take 1.75 hours (or 1 hour 45 minutes) for the airplanes to be 1925 km apart. 7. **Problem 2:** Two cars start from the same place traveling in opposite directions. One car travels 4 mph faster than the other. After 5 hours, they are 520 miles apart. Find their speeds. 8. Let the speed of the slower car be $x$ mph. Then the faster car's speed is $x + 4$ mph. 9. Using $d = rt$, total distance after 5 hours is: $$5x + 5(x + 4) = 520$$ 10. Simplify: $$5x + 5x + 20 = 520$$ 11. Combine like terms: $$10x + 20 = 520$$ 12. Subtract 20: $$10x = 500$$ 13. Solve for $x$: $$x = 50$$ 14. Speeds are 50 mph and 54 mph. 15. **Answer:** The slower car travels at 50 mph, and the faster car at 54 mph.