Final answer:
The wave is travelling at a velocity of 18 m/s.
Step-by-step explanation:
The wave velocity can be calculated using the formula
V = f * λ,
where V is the velocity, f is the frequency, and λ is the wavelength.
In this case, the frequency is 9 Hz and the wavelength is 2 m.
Substituting these values into the formula, we get:
V = 9 Hz * 2 m = 18 m/s
Therefore, the wave is travelling at a velocity of 18 m/s.