To solve the exercise it is necessary to take into account the concepts of wavelength as a function of speed.
From the definition we know that the wavelength is described under the equation,
[tex]\lambda = \frac{c}{f}[/tex]
Where,
c = Speed of light (vacuum)
f = frequency
Our values are,
[tex]f = 2Hz[/tex]
[tex]c = 3*10^8km/s[/tex]
Replacing we have,
[tex]\lambda = \frac{c}{f}[/tex]
[tex]\lambda = \frac{3*10^8km/s}{2Hz}[/tex]
[tex]\lambda = 1.5*10^8m[/tex]
Therefore the wavelength of this wave is [tex]1.5*10^{8}m[/tex]
