1) Hearing the siren of an approaching fire truck, you pull over
to the side of the road and stop. As the truck approaches, you hear
a tone of 451 Hz; as the truck recedes, you hear a tone of 410 Hz.
How much time will it take for the truck to get from your position
to the fire 6.5 km away, assuming it maintains a constant
speed?

2)Two cars traveling with the same speed move directly away from
one another. One car sounds a horn whose frequency is 165 Hz and a
person in the other car hears a frequency of 153 Hz. What is the
speed of the cars?