Answer:
I'll assume that "no frequency of 3.50 Hz" is supposed to read "a c frequency of 3.50 Hz"
Explanation:
A wave's speed is given by Speed = Distance/Time.
In this case the distance and time are provided: The wavelength is 1.75cm and the time between each wave is (1/3.50) seconds/cycle. That is, the wave travels 1.75 cm every (1/3.50) or 0.2857 seconds. The amplitude has no bearing on this calculation, unless it is 6.5 km high and in your lab.
In that case we'd like to know how much time we have before it reaches us across the 10 m room.
(Distance)/(Time) = 1.75 cm)/(0.2857 sec) = 6.125 cm/second is the speed of the wave.
For a 10 meter room (1000 cm), that would give us (1000cm)/(6.125 cm/sec) = 163 seconds to reach and close the exit door.
