This can be answered using the beat frequency formula, which is simply the difference between 2 frequencies.
Let: fᵇ = beat frequency
f₁ = first frequency
f₂ = second frequency
fᵇ = |f₁ - f₂|
substituting the values:
fᵇ = |24Hz - 20Hz|
fᵇ = 4Hz
The unit Hz also means beats per second, therefore:
fᵇ = 4 beats per second
Therefore, the answer is C. 4
