Answer:
0.25 Hz (Hertz).
Step-by-step explanation:
To calculate the frequency of a wave, you can use the formula:
Frequency (f) = Number of Waves / Time
In your case, you have 5 waves in 20 seconds:
Frequency (f) = 5 waves / 20 seconds = 0.25 waves per second
So, the frequency is 0.25 Hz (Hertz).