Each of two adjacent loudspeakers produces a pure note
(a single frequency sound wave). A microphone in the same room
detects the sound intensity as a function of time and the
result is plotted on an oscilloscope as a function of time, as
pictured in the graph below. [Note: ms = milliseconds.]
From the graph, estimate the frequency
of each of the two transmitters.
Express your answer in kHz [kilohertz].