Answer:
4.05 m/s
Explanation:
Frequency f and wavelength lambda are related to each other through the propagation speed v as shown below. That allows us to caclulate the speed when f and lambda are known:
[tex]f = \frac{v}{\lambda}\implies v = f\lambda=4.5\frac{1}{s}0.9m=4.05\frac{m}{s}[/tex]
The speed of the wave is 4.05 m/s.