Answer: 0 km/h
Explanation:
As a vector, the plane's velocity is 100 km/h (west) - 100 km/h (east) = 0 km/m.
To an observer on the ground, the plane will be standing still.
Answer:
<u><em>A. wavelength</em></u>
Explanation:
The others are about sound and how high it is. That has nothing to do with time.