You are holding a siren, and you hear a frequency of 1200 Hz from it when you are standing still. You now move directly toward a cliff wall at a speed of 1/5 the speed of sound. What frequency do you hear as an echo from the cliff wall?

Explanation:

From the question we are told that:

Frequency

Speed

Where speed of sound

Generally the equation for frequency  that echo from the cliff wall is mathematically given by

the total distance traveled by the car is

30km + 49km = 79 km .

the total distance that martina travels that day is

(distance from home to mom's office) plus (distance from mom's office to school)

plus (distance from school to library) plus (distance from library to friend's house)

plus (distance from friend's house to martina's house).

(we don't know what any of these distance actually is.)