The temperature is dropping throughout the day as a cold front comes in. In City A, the temperature is changing by −5°F per hour, and in City B the temperature is changing by −3°F per hour. If the temperatures in both cities started at 70°F, which city is warmer, and what is the difference in their temperatures after 5 hours?
In City A, the temperature is changing by -5°F per hour. After 5 hours, the change in temperature is -5°F * 5 = -<<-5*5=-25>>25°F.
The temperature in City A after 5 hours is 70°F - 25°F = 45°F.
In City B, the temperature is changing by -3°F per hour. After 5 hours, the change in temperature is -3°F * 5 = -<<-3*5=-15>>15°F.
The temperature in City B after 5 hours is 70°F - 15°F = 55°F.
Therefore, City B is warmer by 55°F - 45°F = 10°F. Answer: \boxed{10}.