Answer:
3.77 Hz
Step-by-step explanation:
The beat frequency that is heard can be calculated using the following equation:

Where:
f₁ = 110 Hz

With:
T₁ = 594 N
T₂ = 554 N
Hence, the beat frequency is:
Therefore, the beat frequency that is heard when the hammer strikes the two strings simultaneously is 3.77 Hz.
I hope it helps you!