The speed of the wave is 0.06 m/s.
The speed of a wave can be calculated using the formula:
speed = wavelength x frequency
In this case, the wavelength is 15 mm and the frequency is 4.0 Hz.
Converting mm to meters, we have 15 mm = 0.015 m.
Plugging in the values, we get:
speed = 0.015 m x 4.0 Hz = 0.06 m/s
So, the speed of the wave is 0.06 m/s.