The speed of a wave is given by this formula
v = f × λ
where:
v is the speed = 5 km/s
f is the frequency = 11 Hz
λ is the wavelength (in metres)
We need to convert the speed into meters
5 km/s = 5000 m/s
Then substitute these values into the formula:
5000 = 11 × λ
λ = 5000 ÷ 11
λ = 454.5 meters